Use of ceramics in dental and orthodontic applications

ABSTRACT

The invention relates to uses of glasses and glass-ceramics in dental and orthodontic applications.

BACKGROUND

[0001] The invention relates to uses of ceramics in dental andorthodontic applications.

[0002] Although performance and durability are highly desirablecharacteristics for dental replacement and repair work, for example,they alone are not the sole concern for practitioners and patients.Aesthetic value, or how dental materials and articles and orthodonticappliances look inside the mouth is just as desirable.

[0003] For example, in prosthodontics and restorative dentistry, wheretooth replacement or prostheses are custom made to fit in or on a toothstructure, there are instances where the restoration or repair can beseen from a short distance when the mouth is open. Thus in thoseinstances, it would be highly desired that the dental material be nearlyindistinguishable from adjacent tooth structure.

[0004] Prosthetics and restorative dentistry encompass the fabricationand installation of, for example, restoratives, replacements, inlays,onlays, veneers, full and partial crowns, bridges, implants, and posts.Conventional materials used to make dental prostheses include gold,ceramics, amalgam, porcelain, and composites. In terms of aestheticvalue, it is perceived that porcelains, composites, and ceramics lookbetter than amalgam and metals, since a prosthetic made from thosenonmetals better matches or blends in with the color of adjacent naturalteeth.

[0005] For orthodontic appliances (typically, brackets, which are smallslotted bodies for holding a curved arch wire, and associated toothbands if banded attachment is used), stainless steel is an idealmaterial because it is strong, nonabsorbent, weldable, and relativelyeasy to form and machine. A significant drawback of metal appliances,however, relates to cosmetic appearance when the patient smiles. Adultsand older children undergoing orthodontic treatment are oftenembarrassed by the “metallic smile” appearance of metal bands andbrackets, and this problem has led to various improvements in recentyears.

[0006] One area of improvement involves use of nonmetal materials. Bothplastic and ceramic materials present an improved appearance in themouth, and often the only significantly visible metal components arethin arch wires that are cosmetically acceptable. Plastic is not anideal material because it lacks the structural strength of metal, and issusceptible to staining and other problems. Ceramics such as sapphire orother transparent crystalline materials have undesirable prismaticeffects. Also, single crystal aluminum oxide appliances are subject tocleavage under the loads that occur in the course of orthodontictreatment. Other ceramics have been largely opaque so that they eitherdo not match tooth color or require coloring.

[0007] Glasses and glass-ceramics have also been used for dentalreplacement and repair work. Sinterable glass-ceramics based on lithiumdisilicate utilized in production of shaped dental products are known.For example, some compositions are based on SiO₂ (57-80 wt-%) and Li₂O(11-19 wt-%) with minor amounts of Al₂O₃, La₂O₃, MgO, ZnO, K₂O, P₂O₅ andother materials. Another examples are moldable ceramic-glasscompositions which include 50-99 parts by weight of alumina and/orzirconia powder and 1 to 50 parts by weight of glass powder.

[0008] Digitized machining of ceramics (commonly known as CAD/CAMmilling) is one method for producing useful dental shapes. However, themachining of fully densified structural ceramics like Al₂O₃ and ZrO₂into complex dental geometries is difficult due to rapid tool wear. Forthis reason, methods involving machining of green ceramic body have beendeveloped (e.g. LAVA ZrO₂ by 3M Company).

SUMMARY

[0009] In one embodiment, the invention provides an article comprising aceramic in the form of a dental article or an orthodontic appliancewherein the ceramic comprises at least one of a ceramic, glass, orglass-ceramic comprising:

[0010] a) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the glass or glass-ceramic contains not more than 10 percent byweight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass or glass-ceramic;

[0011] b) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the Al₂O₃ and the first metal oxide collectively comprise atleast 70 percent by weight of the glass or glass-ceramic;

[0012] c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, based on the total weightof the glass or glass-ceramic;

[0013] d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weight of theglass or glass-ceramic;

[0014] e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0015] f) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0016] g) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic comprise the Al₂O₃ andthe at least one of REO or Y₂O₃, and wherein the glass or glass-ceramiccontains not more than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass or glass-ceramic;

[0017] h) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or

[0018] i) a glass-ceramic having an average hardness of at least 13 GPa,wherein the glass-ceramic has x, y, and z dimensions each perpendicularto each other, and wherein each of the x, y, and z dimensions is atleast 5 mm.

[0019] In another embodiment, the invention provides a dental materialcomprising a mixture of a hardenable resin and a ceramic comprising atleast one of a glass or glass-ceramic comprising:

[0020] a) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the glass or glass-ceramic contains not more than 10 percent byweight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass or glass-ceramic;

[0021] b) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the Al₂O₃ and the first metal oxide collectively comprise atleast 70 percent by weight of the glass or glass-ceramic;

[0022] c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, based on the total weightof the glass or glass-ceramic;

[0023] d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weight of theglass or glass-ceramic;

[0024] e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0025] f) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0026] g) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic comprise the Al₂O₃ andthe at least one of REO or Y₂O₃, and wherein the glass or glass-ceramiccontains not more than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass or glass-ceramic;

[0027] h) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or

[0028] i) a glass-ceramic having an average hardness of at least 13 GPa.

[0029] In another embodiment, the invention provides a method of makinga dental article or an orthodontic appliance comprising the steps of:

[0030] providing a dental or orthodontic mill blank;

[0031] carving a dental or orthodontic mill blank, wherein the millblank comprises a glass or glass-ceramic comprising at least one of:

[0032] a) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the glass or glass-ceramic contains not more than 10 percent byweight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass or glass-ceramic;

[0033] b) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃wherein the Al₂O₃ and the first metal oxide collectively comprise atleast 70 percent by weight of the glass or glass-ceramic;

[0034] c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, based on the total weightof the glass or glass-ceramic;

[0035] d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weight of theglass or glass-ceramic;

[0036] e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0037] f) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0038] g) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic comprise the Al₂O₃ andthe at least one of REO or Y₂O₃, and wherein the glass or glass-ceramiccontains not more than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass or glass-ceramic;

[0039] h) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or

[0040] i) a glass-ceramic having an average hardness of at least 13 GPa.

[0041] In another embodiment, the invention provides a method of makinga dental article or an orthodontic appliance comprising the steps of:

[0042] heating glass above the T_(g) of the glass such that the glasscoalesces or flows to form a dental article or an orthodontic appliancehaving a shape; and

[0043] cooling the coalesced article, wherein the glass comprises atleast one of:

[0044] a) at least 35 percent by weight Al₂O₃, based on the total weightof the glass, and a first metal oxide other than Al₂O₃, wherein theceramic contains not more than 10 percent by weight collectively B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass;

[0045] b) at least 35 percent by weight Al₂O₃, based on the total weightof the glass, a first metal oxide other than Al₂O₃, wherein the Al₂O₃and the first metal oxide collectively comprise at least 70 percent byweight of the glass;

[0046] c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80percent by weight of the glass collectively comprises the Al₂O₃ and theat least one of REO or Y₂O₃, based on the total weight of the glass;

[0047] d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass;

[0048] e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass collectively comprises the Al₂O₃ and theat least one of REO or Y₂O₃, and wherein the glass contains not morethan 20 percent by weight SiO₂ and not more than 20 percent by weightB₂O₃, based on the total weight of the glass;

[0049] f) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, and wherein the glass contains not more than 20 percent byweight SiO₂ and not more than 20 percent by weight B₂O₃, based on thetotal weight of the glass;

[0050] g) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass comprise the Al₂O₃ and the at least oneof REO or Y₂O₃, and wherein the glass contains not more than 40 percentby weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weightof the glass; or

[0051] h) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, and wherein the glass contains not more than 40 percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe glass.

[0052] In another embodiment, the invention provides a method of makinga dental article or an orthodontic appliance comprising the steps of:

[0053] combining a glass or glass-ceramic with a hardenable resin toform a mixture;

[0054] forming the dental article or the orthodontic appliance into ashape; hardening said mixture to form the dental article or orthodonticappliance, wherein said glass or glass-ceramic comprises at least oneof:

[0055] a) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the glass or glass-ceramic contains not more than 10 percent byweight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass or glass-ceramic;

[0056] b) at least 35 percent by weight Al₂O₃, based on the total weightof the glass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the Al₂O₃ and the first metal oxide collectively comprise atleast 70 percent by weight of the glass or glass-ceramic;

[0057] c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, based on the total weightof the glass or glass-ceramic;

[0058] d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weight of theglass or glass-ceramic;

[0059] e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0060] f) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic;

[0061] g) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass or glass-ceramic comprise the Al₂O₃ andthe at least one of REO or Y₂O₃, and wherein the glass or glass-ceramiccontains not more than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass or glass-ceramic;

[0062] h) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or

[0063] i) a glass-ceramic having an average hardness of at least 13 GPa.

[0064] In another embodiment, the invention provides a method of makinga dental article or orthodontic appliance comprising the steps of:

[0065] plasma or thermally spraying particles comprising metal oxidesources onto a suitable substrate such that the particles coalesce toform a shaped article; and optionally separating the shaped article orappliance from the substrate, wherein the shaped article comprises atleast one of:

[0066] a) at least 35 percent by weight Al₂O₃, based on the total weightof the glass, and a first metal oxide other than Al₂O₃, wherein theglass contains not more than 10 percent by weight collectively B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass;

[0067] b) at least 35 percent by weight Al₂O₃, based on the total weightof the glass, and a first metal oxide other than Al₂O₃, wherein theAl₂O₃ and the first metal oxide collectively comprise at least 70percent by weight of the glass;

[0068] c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80percent by weight of the glass collectively comprises the Al₂O₃ and theat least one of REO or Y₂O₃, based on the total weight of the glass;

[0069] d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass;

[0070] e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass collectively comprises the Al₂O₃ and theat least one of REO or Y₂O₃, and wherein the glass contains not morethan 20 percent by weight SiO₂ and not more than 20 percent by weightB₂O₃, based on the total weight of the glass;

[0071] f) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, and wherein the glass contains not more than 20 percent byweight SiO₂ and not more than 20 percent by weight B₂O₃, based on thetotal weight of the glass;

[0072] g) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60percent by weight of the glass comprise the Al₂O₃ and the at least oneof REO or Y₂O₃, and wherein the glass contains not more than 40 percentby weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weightof the glass; or

[0073] h) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, and wherein the glass contains not more than 40 percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe glass.

[0074] In another embodiment, the invention provides a kit comprising aplurality of dental or orthodontic components wherein at least one ofthe components includes a dental material, dental article, ororthodontic appliance comprising at least one of a glass orglass-ceramic described herein.

[0075] In another embodiment, the invention provides a method ofperforming a dental restoration comprising the steps of: preparing adental site to be restored; and

[0076] applying a restorative material comprising at least one of aceramic, glass, or glass-ceramic described herein.

BRIEF DESCRIPTION OF THE FIGURES

[0077]FIG. 1 is a digital image of an optical photomicrograph of ahot-pressed ceramic.

[0078]FIG. 2a is a digital image of a scanning electron microscope (SEM)photomicrograph of a polished section of Example 1 material heat-treatedat 1300° C.

[0079]FIG. 2b is a digital image of a scanning electron microscope (SEM)photomicrograph of a polished section of Example 1 material heat-treatedat 1400° C.

[0080]FIG. 3 is a DTA trace for Example 1 material.

[0081]FIG. 4 is a photograph of a dental restoration milled usingExample 1 material and a comparative dental restoration milled usingstandard (PARADIGM MZ100) material.

DETAILED DESCRIPTION

[0082] In this application:

[0083] “amorphous material” refers to material derived from a meltand/or a vapor phase that lacks any long range crystal structure asdetermined by x-ray diffraction and/or has an exothermic peakcorresponding to the crystallization of the amorphous material asdetermined by a DTA (differential thermal analysis) as determined by thetest described herein entitled “Differential Thermal Analysis”;

[0084] “ceramic” includes amorphous material, glass, crystallineceramic, glass-ceramic, and combinations thereof;

[0085] “complex metal oxide” refers to a metal oxide comprising two ormore different metal elements and oxygen (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂,MgA₁₂O₄, and Y₃Al₅O₁₂);

[0086] “complex Al₂O₃.metal oxide” refers to a complex metal oxidecomprising, on a theoretical oxide basis, Al₂O₃ and one or more metalelements other than Al (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂, MgA_(l2)O₄, andY₃Al₅O₁₂);

[0087] “complex Al₂O₃.Y₂O₃” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and Y₂O₃ (e.g., Y₃Al₅O₁₂);

[0088] “complex Al₂O₃.REO” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and rare earth oxide (e.g.,CeAl₁₁O₁₈ and Dy₃Al₅O₁₂);

[0089] “dental article” refers to a restored dentition or a portionthereof. Examples include restoratives, replacements, inlays, onlays,veneers, full and partial crowns, bridges, implants, implant abutments,copings, anterior fillings, posterior fillings, cavity liners, sealants,dentures, posts, and bridge frameworks;

[0090] “dental material” refers to a dental composition such as a pastewhich when hardens forms a dental article;

[0091] “glass” refers to amorphous material exhibiting a glasstransition temperature;

[0092] “glass-ceramic” refers to ceramics comprising crystals formed byheat-treating amorphous material;

[0093] “hardenable” refers to a material that can be cured or solidified(e.g., by heating to remove solvent, heating to cause polymerization,chemical crosslinking, radiation-induced polymerization or crosslinking,or the like);

[0094] “hardened” refers to material that is cured or solidified (e.g.,by heating to remove solvent, heating to cause polymerization, chemicalcrosslinking, radiation-induced polymerization or crosslinking, or thelike);

[0095] “hardening” refers to a method of curing or solidifying (e.g., byheating to remove solvent, heating to cause polymerization, chemicalcrosslinking, radiation-induced polymerization or crosslinking, or thelike);

[0096] “orthodontic appliance” refers to any device intended formounting on a tooth, and used to transmit to the tooth corrective forcefrom an arch wire, spring, elastic, or other force-applying component.Examples include brackets, buccal tubes, cleats, and buttons;

[0097] “prosthesis” includes crowns, bridges, inlays, onlays, veneers,copings, frameworks, and abutments;

[0098] “restoratives” includes veneers, crowns, inlays, onlays, andbridge structures;

[0099] “T_(g)” refers to the glass transition temperature as determinedby the test described herein entitled “Differential Thermal Analysis”;

[0100] “T_(x)” refers to the crystallization temperature as determinedby the test described herein entitled “Differential Thermal Analysis”;

[0101] “rare earth oxides” refers to cerium oxide (e.g., CeO₂),dysprosium oxide (e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europiumoxide (e.g., Eu₂O₃), gadolinium (e.g., Gd₂O₃), holmium oxide (e.g.,Ho₂O₃), lanthanum oxide (e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃),neodymium oxide (e.g., Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁),samarium oxide (e.g., Sm₂O₃), terbium (e.g., Tb₂O₃), thorium oxide(e.g., Th₄O₇), thulium (e.g., Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃),and combinations thereof; and

[0102] “REO” refers to rare earth oxide(s).

[0103] Further, it is understood herein that unless it is stated that ametal oxide (e.g., Al₂O₃, complex Al₂O₃.metal oxide, etc.) iscrystalline, for example, in a glass-ceramic, it may be amorphous,crystalline, or portions amorphous, and portions crystalline. Forexample, if a glass-ceramic comprises Al₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂may each be in an amorphous state, crystalline state, or portions in anamorphous state and portions in a crystalline state, or even as areaction product with another metal oxide(s) (e.g., unless it is statedthat, for example, Al₂O₃ is present as crystalline Al₂O₃ or a specificcrystalline phase of Al₂O₃ (e.g., alpha Al₂O₃), it may be present ascrystalline Al₂O₃ and/or as part of one or more crystalline complexAl₂O₃.metal oxides).

[0104] Further, it is understood that glass-ceramics formed by heatingamorphous material not exhibiting a T_(g) may not actually compriseglass, but rather may comprise the crystals and amorphous material thatdoes not exhibiting a T_(g).

[0105] Some advantages of using the ceramics, glasses, andglass-ceramics described herein for dental and orthodontic applicationsinclude improved processing abilities of complex-shaped articlescombined with excellent material properties that are akin to those ofstructural ceramics (e.g., Al₂O₃ and ZrO₂). These useful dental shapescan be generated by either glass-like viscous flow or by machiningblanks in amorphous or partially crystalline states.

[0106] Ceramics, Glass, and Glass-Ceramics

[0107] In some embodiments according to the present invention, theceramic, the glass and the glass-ceramic comprises at least 35 (in someembodiments, at least 40, 45, 50, 55, 60, 65, 70, or even at least 75)percent by weight Al₂O₃, based on the total weight of the ceramic,glass, or glass-ceramic, respectively, and a first metal oxide otherthan Al₂O₃ (e.g., Y₂O₃, REO, MgO, TiO₂, Cr₂O₃, CuO, NiO, and Fe₂O₃), andoptionally a second, (third, etc.) different metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, MgO, TiO₂, Cr₂O₃, CuO, NiO, and, Fe₂O₃), whereinthe glass or glass-ceramic, respectively, contains not more than 10 (insome embodiments, not more than 5, 4, 3, 2, 1, or zero) percent byweight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass or glass-ceramic, respectively. Embodiments ofthe glass-ceramic have an average hardness of at least 13 GPa, 14 GPa,15 GPa, 16 GPa, 17 GPa, 18 GPa, or even at least 19 GPa.

[0108] In some embodiments according to the present invention, the glassand the glass-ceramic comprises at least 35 (in some embodiments, atleast 40, 45, 50, 55, 60, 65, 70, or even at least 75) percent by weightAl₂O₃, based on the total weight of the ceramic, glass, orglass-ceramic, respectively, and a first metal oxide other than Al₂O₃(e.g., Y₂O₃, REO, MgO, TiO₂, Cr₂O₃, CuO, NiO, and Fe₂O₃), andoptionally, a second, (third etc.) different metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, MgO, TiO₂, Cr₂O₃, CuO, NiO, and, Fe₂O₃), whereinthe Al₂O₃, first metal oxide, and second metal oxide collectivelycomprise at least 80 (in some embodiments, at least 85, 90, 95, or 100)percent by weight of the ceramic, glass, or glass-ceramic, respectively,and wherein the ceramic, glass, or glass-ceramic contains not more than20 (in some embodiments, not more than 15, 10, 5, 4, 3, 2, 1, or evenzero) percent by weight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, andV₂O₅, based on the total weight of the ceramic, glass, or glass-ceramic,respectively. Embodiments of the glass-ceramic have an average hardnessof at least 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, 18 GPa, or even atleast 19 GPa.

[0109] In some embodiments according to the present invention, theceramic, the glass, and the glass-ceramic comprises Al₂O₃ and at leastone of REO or Y₂O₃, wherein at least 80 (in some embodiments, at least85, 90, 95, or even 100) percent by weight of the ceramic, glass, orglass-ceramic, respectively, collectively comprises the Al₂O₃ and the atleast one of REO or Y₂O₃, based on the total weight of the ceramic,glass, or glass-ceramic, respectively.

[0110] In some embodiments according to the present invention, theceramic, the glass, and the glass-ceramic comprises Al₂O₃, at least oneof REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80(in some embodiments, at least 85, 90, 95, or even 100) percent byweight of the ceramic, glass, or glass-ceramic, respectively,collectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, based on the total weight of the ceramic,glass, or glass-ceramic, respectively. Embodiments of the glass-ceramichave an average hardness of at least 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17GPa, 18 GPa, or even at least 19 GPa.

[0111] In some embodiments according to the present invention, theceramic, the glass, and the glass-ceramic comprises Al₂O₃ and at leastone of REO or Y₂O₃, wherein at least 60 (in some embodiments, 65, 70,75, 80, 85, 90, 95, or even at least 100) percent by weight of theceramic, glass, or glass-ceramic, respectively, collectively comprisesthe Al₂O₃ and the at least one of REO or Y₂O₃, and wherein the ceramic,glass, or glass-ceramic, respectively, contains not more than 20 (insome embodiments, not more than 15, 10, 5, or even zero) percent byweight SiO₂ and not more than 20 (in some embodiments, not more than 15,10, 5, or even zero) percent by weight B₂O₃, based on the total weightof the ceramic, glass, or glass-ceramic, respectively. Embodiments ofthe glass-ceramic have an average hardness of at least 13 GPa, 14 GPa,15 GPa, 16 GPa, 17 GPa, 18 GPa, or even at least 19 GPa.

[0112] In some embodiments according to the present invention, theceramic, the glass, and the glass-ceramic comprises Al₂O₃, at least oneof REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60(in some embodiments, 65, 70, 75, 80, 85, 90, 95, or even at least 100)percent by weight of the ceramic, glass, or glass-ceramic, respectively,collectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, and wherein the ceramic, glass, orglass-ceramic, respectively, contains not more than 20 (in someembodiments, less than 15, 10, 5, or even zero) percent by weight SiO₂and not more than 20 (in some embodiments, not more than 15, 10, 5, oreven zero) percent by weight B₂O₃, based on the total weight of theceramic, glass, or glass-ceramic, respectively. Embodiments of theglass-ceramic have an average hardness of at least 13 GPa, 14 GPa, 15GPa, 16 GPa, 17 GPa, 18 GPa, or even at least 19 GPa.

[0113] In some embodiments according to the present invention, theceramic, the glass, and the glass-ceramic comprises Al₂O₃ and at leastone of REO or Y₂O₃, wherein at least 60 (in some embodiments, 65, 70,75, 80, 85, 90, 95, or even at least 100) percent by weight of theceramic, glass, or glass-ceramic, respectively, comprise the Al₂O₃ andthe at least one of REO or Y₂O₃, and wherein the ceramic, glass, orglass-ceramic, respectively, contains not more than 40 (in someembodiments, not more than 35, 30, 25, 20, 15, 10, 5, or even zero)percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the totalweight of the ceramic, glass, or glass-ceramic, respectively.Embodiments of the glass-ceramic have an average hardness of at least 13GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, 18 GPa, or even at least 19 GPa.

[0114] In some embodiments according to the present invention, theceramic, the glass, and the glass-ceramic comprises Al₂O₃, at least oneof REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60(in some embodiments, 65, 70, 75, 80, 85, 90, 95, or even at least 100)percent by weight of the ceramic, glass, or glass-ceramic, respectively,collectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, and wherein the ceramic, glass, orglass-ceramic, respectively, contains not more than 40 (in someembodiments, not more than 35, 30, 25, 20, 15, 10, 5, or even zero)percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the totalweight of the ceramic, glass, or glass-ceramic, respectively.Embodiments of the glass-ceramic have an average hardness of at least 13GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, 18 GPa, or even at least 19 GPa.

[0115] Some embodiments of glass-ceramics according to the presentinvention may comprise, for example, at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100percent by volume glass. Some embodiments of glass-ceramics according tothe present invention may comprise, for example, at least 1, 2, 3, 5,10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95,97, 98, 99, or even 100 percent by volume crystalline ceramic, based onthe total volume of the glass-ceramic.

[0116] Some amorphous materials used to make glasses and theglass-ceramics made therefrom, comprise 20 to at least 70 percent byweight (in some embodiments, 30 to at least 70 percent, 40 to at least70 percent, 50 to at least 70 percent, or even 60 to at least 70percent) Al₂O₃; 0 to 70 percent by weight (in some embodiments, 0 to 25percent, or even 0 to 10 percent) Y₂O₃; and 0 to 70 percent by weight(in some embodiments, 0 to 50 percent, 0 to 25 percent, or even 0 to 10percent) at least one of ZrO₂ or HfO₂, based on the total weight of theamorphous material or glass-ceramic. In some embodiments, such amorphousmaterials, and the glass-ceramics made therefrom, comprise at least 30percent by weight, at least 40 percent by weight, at least 50 percent byweight, at least 60 percent by weight, or even at least 70 percent byweight Al₂O₃, based on the total weight of the amorphous material orglass-ceramic. In some embodiments, such amorphous materials, and theglass-ceramics made therefrom, contain less than 40 (in someembodiments, less than 35, 30, 25, 20, 15, 10, 5, 4, 3, 2, 1, or evenzero) percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on thetotal weight of the amorphous material or glass-ceramic. In someembodiments, such amorphous materials, and the glass-ceramics madetherefrom, contain less than 20 (in some embodiments, less than 15, 10,5, or even zero) percent by weight SiO₂ and less than 20 (preferably,less than 15, 10, 5, or even zero) percent by weight B₂O₃, based on thetotal weight of the amorphous material or glass-ceramic.

[0117] Some amorphous materials used to make glasses and theglass-ceramics made therefrom, comprise 20 to at least 70 percent byweight (in some embodiments, 30 to at least 70 percent, 40 to at least70 percent, 50 to at least 70 percent, or even 60 to at least 70percent) Al₂O₃; 0 to 70 percent by weight (in some embodiments, 0 to 50percent, 0 to 25 percent, or even 0 to 10 percent) REO; 0 to 50 percentby weight (in some embodiments, 0 to 25 percent, or even 0 to 10percent) at least one of ZrO₂ or HfO₂, based on the total weight of theamorphous material or glass-ceramic. In some embodiments, such amorphousmaterials, and the glass-ceramics made therefrom, comprise 30 percent byweight, at least 40 percent by weight, at least 50 percent by weight, atleast 60 percent by weight, or even at least 70 percent by weight Al₂O₃,based on the total weight of the amorphous material or glass-ceramic. Insome embodiments, such amorphous materials, and the glass-ceramics madetherefrom, comprise less than 40 (in some embodiments, less than 35, 30,25, 20, 15, 10, 5, 4, 3, 2, 1, or even zero) percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theamorphous materials or glass-ceramic. In some embodiments, such glasses,and the glass-ceramics made therefrom, contain less than 20 (in someembodiments, less than 15, 10, 5, or even zero) percent by weight SiO₂and less than 20 (in some embodiments, less than 15, 10, 5, or evenzero) percent by weight B₂O₃, based on the total weight of the amorphousmaterial or glass-ceramic.

[0118] Some amorphous materials used to make glasses and theglass-ceramics made therefrom, comprise 20 to at least 70 percent byweight (in some embodiments, 30 to at least 70 percent, 40 to at least70 percent, 50 to at least 70 percent, or even 60 to 70 percent) Al₂O₃;0 to 70 percent by weight (in some embodiments, 0 to 50 percent, 0 to 25percent, or even 0 to 10 percent) Y₂O₃; 0 to 70 percent by weight (insome embodiments, 0 to 50 percent, 0 to 25 percent, or even 0 to 10percent) REO; 0 to 50 percent by weight (in some embodiments, 0 to 25percent, or even 0 to 10 percent) at least one of ZrO₂ or HfO₂, based onthe total weight of the amorphous material or glass-ceramic. In someembodiments, such amorphous materials, and the glass-ceramics madetherefrom, comprise at least 30 percent by weight, at least 40 percentby weight, at least 50 percent by weight, at least 60 percent by weight,or even at least 70 percent by weight Al₂O₃, based on the total weightof the amorphous material or glass-ceramic. In some embodiments, suchamorphous materials, and the glass-ceramics made therefrom, contain lessthan 40 (in some embodiments, less than 35, 30, 25, 20, 15, 10, 5, 4, 3,2, 1, or even zero) percent by weight collectively SiO₂, B₂O₃, and P₂O₅,based on the total weight of the amorphous material or glass-ceramic. Insome embodiments, such amorphous materials, and the glass-ceramics madetherefrom, contain less than 20 (in some embodiments, less than 15, 10,5, or even zero) percent by weight SiO₂ and less than 20 (in someembodiments, less than 15, 10, 5, or even zero) percent by weight B₂O₃,based on the total weight of the amorphous material or glass-ceramic.

[0119] Amorphous materials (e.g., glasses), ceramics comprising theamorphous material, particles comprising the amorphous material, etc.can be made, for example, by heating (including in a flame) theappropriate metal oxide sources to form a melt, desirably a homogenousmelt, and then rapidly cooling the melt to provide amorphous material.The metal oxide sources and other additives can be in any form suitableto the process and equipment used to make the glass or glass-ceramics.Desirable cooling rates include those of 10 K/s and greater. Embodimentsof amorphous materials can be made, for example, by melting the metaloxide sources in any suitable furnace (e.g., an inductive heatedfurnace, a gas-fired furnace, or an electrical furnace), or, forexample, in a plasma. The resulting melt is cooled (e.g., dischargingthe melt into a cooling media (e.g., high velocity air jets, liquids,metal plates (including chilled metal plates), metal rolls (includingchilled metal rolls), metal balls (including chilled metal balls), andthe like)).

[0120] Further, other techniques for making melts and glasses, andotherwise forming amorphous material include vapor phase quenching,melt-extraction, plasma spraying, and gas or centrifugal atomization.For additional details regarding plasma spraying, see, for example,copending application having U.S. application Ser. No. 10/211,640, filedAug. 2, 2002, the disclosure of which is incorporated herein byreference.

[0121] Gas atomization involves melting feed particles to convert themto melt. A thin stream of such melt is atomized through contact with adisruptive air jet (i.e., the stream is divided into fine droplets). Theresulting substantially discrete, generally ellipsoidal amorphousmaterial comprising particles (e.g., beads) are then recovered. Examplesof bead sizes include those having a diameter in a range of about 5micrometers to about 3 mm. Melt-extraction can be carried out, forexample, as disclosed in U.S. Pat. No. 5,605,870, the disclosure ofwhich is incorporated herein by reference. Containerless glass formingtechniques utilizing laser beam heating as disclosed, for example, inU.S. Pat. No. 6,482,758, the disclosure of which is incorporated hereinby reference, may also be useful in making glass, glass-ceramics andamorphous materials.

[0122] Embodiments of amorphous material can be made utilizing flamefusion as disclosed, for example, in U.S. Pat. No. 6,254,981, thedisclosure of which is incorporated herein by reference. In this method,the metal oxide sources materials are fed (e.g., in the form ofparticles, sometimes referred to as “feed particles”) directly into aburner (e.g., a methane-air burner, an acetylene-oxygen burner, ahydrogen-oxygen burner, and like), and then quenched, for example, inwater, cooling oil, air, or the like. Feed particles can be formed, forexample, by grinding, agglomerating (e.g., spray-drying), melting, orsintering the metal oxide sources. The size of feed particles fed intothe flame generally determine the size of the resulting amorphousmaterial comprising particles.

[0123] Embodiments of amorphous materials can also be obtained by othertechniques, such as: laser spin melt with free fall cooling, Taylor wiretechnique, plasmatron technique, hammer and anvil technique, centrifugalquenching, air gun splat cooling, single roller and twin rollerquenching, roller-plate quenching and pendant drop melt extraction (see,e.g., Rapid Solidification of Ceramics, Brockway et. al, Metals AndCeramics Information Center, A Department of Defense InformationAnalysis Center, Columbus, Ohio, January, 1984, the disclosure of whichis incorporated here as a reference). Embodiments of amorphous materialsmay also be obtained by other techniques, such as: thermal (includingflame or laser or plasma-assisted) pyrolysis of suitable precursors,physical vapor synthesis (PVS) of metal precursors and mechanochemicalprocessing.

[0124] The cooling rate is believed to affect the properties of thequenched amorphous material. For instance, glass transition temperature,density, and other properties of glass typically change with coolingrates.

[0125] Rapid cooling may also be conducted under controlled atmospheres,such as a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence amorphous material formation byinfluencing crystallization kinetics from undercooled liquid. Forexample, larger undercooling of Al₂O₃ melts without crystallization hasbeen reported in argon atmosphere as compared to that in air.

[0126] Amorphous materials can also be made by a sol-gel process. Thesol-gel process comprises the steps of forming a precursor compositionin the form of a dispersion, sol, or solution in an aqueous or organicliquid medium. The precursor composition can be processed into a varietyof useful forms including coatings, films, powders, gels, aerogels,dense bulk shapes, fibers, flakes, granules, and nanoclusters. Furtherdetails of these processes can be found in Sol-Gel Science by C. JeffreyBrinker and George W. Scherer (Academic Press, 1990), the disclosure ofwhich is incorporated herein by reference. Further details about thesynthesis of nanoclusters can be found in PCT Publication No. WO0130306(A1), the disclosure of which is incorporated herein byreference. Another method of making powders is by the spray pyrolysis ofa precursor containing one or more glycolato polymetallooxanes dissolvedin a volatile organic solvent; details about this process can be foundin U.S. Pat. No. 5,958,361, the disclosure of which is incorporatedherein by reference.

[0127] Useful amorphous material formulations include those at or near aeutectic composition(s) (e.g., binary and ternary eutecticcompositions). In addition to compositions disclosed herein, othercompositions, including quaternary and other higher order eutecticcompositions, may be apparent to those skilled in the art afterreviewing the present disclosure.

[0128] Sources, including commercial sources, of (on a theoretical oxidebasis) Al₂O₃ include bauxite (including both natural occurring bauxiteand synthetically produced bauxite), calcined bauxite, hydrated aluminas(e.g., boehmite and gibbsite), aluminum, Bayer process alumina, aluminumore, gamma alumina, alpha alumina, aluminum salts, aluminum nitrates,and combinations thereof. The Al₂O₃ source may contain, or only provide,Al₂O₃. Alternatively, the Al₂O₃ source may contain, or provide Al₂O₃, aswell as one or more metal oxides other than Al₂O₃ (including materialsof or containing complex Al₂O₃ metal oxides (e.g., Dy₃Al₅O₁₂, Y₃Al₅O₁₂,CeAl₁₁O₁₈, etc.)).

[0129] Sources, including commercial sources, of rare earth oxidesinclude rare earth oxide powders, rare earth metals, rareearth-containing ores (e.g., bastnasite and monazite), rare earth salts,rare earth nitrates, and rare earth carbonates. The rare earth oxide(s)source may contain, or only provide, rare earth oxide(s). Alternatively,the rare earth oxide(s) source may contain, or provide rare earthoxide(s), as well as one or more metal oxides other than rare earthoxide(s) (including materials of or containing complex rare earth oxidesor other metal oxides (e.g., Dy₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

[0130] Sources, including commercial sources, of (on a theoretical oxidebasis) Y₂O₃ include yttrium oxide powders, yttrium, yttrium-containingores, and yttrium salts (e.g., yttrium carbonates, nitrates, chlorides,hydroxides, and combinations thereof). The Y₂O₃ source may contain, oronly provide, Y₂O₃. Alternatively, the Y₂O₃ source may contain, orprovide Y₂O₃, as well as one or more metal oxides other than Y₂O₃(including materials of or containing complex Y₂O₃.metal oxides (e.g.,Y₃Al₅O₁₂)).

[0131] Sources, including commercial sources, of (on a theoretical oxidebasis) ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

[0132] Other useful metal oxide may also include, on a theoretical oxidebasis, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO, NiO, Na₂O,Sc₂O₃, SrO, TiO₂, ZnO, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides are added to modify a physical property of the resultingparticles and/or improve processing. These metal oxides are typicallyadded anywhere from 0 to 50 percent by weight, in some embodimentspreferably 0 to 25 percent by weight and more preferably 0 to 50 percentby weight of the glass-ceramic depending, for example, upon the desiredproperty.

[0133] The particular selection of metal oxide sources and otheradditives for making ceramics typically takes into account, for example,the desired composition and microstructure of the resulting ceramics,the desired degree of crystallinity, if any, the desired physicalproperties (e.g., hardness or toughness) of the resulting ceramics,avoiding or minimizing the presence of undesirable impurities, thedesired characteristics of the resulting ceramics, and/or the particularprocess (including equipment and any purification of the raw materialsbefore and/or during fusion and/or solidification) being used to preparethe ceramics.

[0134] In some instances, it may be preferred to incorporate limitedamounts of metal oxides selected from the group consisting of: Na₂O,P₂O₅, SiO₂, TeO₂, V₂O₅, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides may be added, for example, to modify a physical property of theresulting particles and/or improve processing. These metal oxides whenused are typically added from greater than 0 to 20 percent by weight,preferably greater than 0 to 5 percent by weight and more preferablygreater than 0 to 2 percent by weight of the glass-ceramic depending,for example, upon the desired property.

[0135] The addition of certain metal oxides may alter the propertiesand/or crystalline structure or microstructure of a glass-ceramic, aswell as the processing of the raw materials and intermediates in makingthe glass-ceramic. For example, oxide additions such as MgO, CaO, Li₂O,and Na₂O have been observed to alter both the T_(g) (for a glass) andT_(x) (wherein T_(x) is the crystallization temperature) of amorphousmaterial. Although not wishing to be bound by theory, it is believedthat such additions influence glass formation. Further, for example,such oxide additions may decrease the melting temperature of the overallsystem (i.e., drive the system toward lower melting eutectic), and easeof amorphous material-formation. Complex eutectics in multi-componentsystems (quaternary, etc.) may result in better amorphousmaterial-forming ability. The viscosity of the liquid melt and viscosityof the glass in its “working” range may also be affected by the additionof certain metal oxides such as MgO, CaO, Li₂O, and Na₂O. It is alsowithin the scope of the present invention to incorporate at least one ofhalogens (e.g., fluorine and chlorine), or chalcogenides (e.g.,sulfides, selenides, and tellurides) into the amorphous materials, andthe glass-ceramics made therefrom.

[0136] Crystallization of the amorphous material and ceramic comprisingthe amorphous material may also be affected by the additions of certainmaterials. For example, certain metals, metal oxides (e.g., titanatesand zirconates), and fluorides, for example, may act as nucleationagents resulting in beneficial heterogeneous nucleation of crystals.Also, addition of some oxides may change nature of metastable phasesdevitrifying from the amorphous material upon reheating. In anotheraspect, for ceramics comprising crystalline ZrO₂, it may be desirable toadd metal oxides (e.g., Y₂O₃, TiO₂, CaO, and MgO) that are known tostabilize tetragonal/cubic form of ZrO₂.

[0137] The microstructure or phase composition(glassy/amorphous/crystalline) of a material can be determined in anumber of ways. Various information can be obtained using opticalmicroscopy, electron microscopy, differential thermal analysis (DTA),and x-ray diffraction (XRD), for example.

[0138] Using optical microscopy, amorphous material is typicallypredominantly transparent due to the lack of light scattering centerssuch as crystal boundaries, while crystalline material shows acrystalline structure and is opaque due to light scattering effects.

[0139] Using DTA, the material is classified as amorphous if thecorresponding DTA trace of the material contains an exothermiccrystallization event (T_(x)). If the same trace also contains anendothermic event (T_(g)) at a temperature lower than T_(x), it isconsidered to consist of a glass phase. If the DTA trace of the materialcontains no such events, it is considered to contain crystalline phases.

[0140] Differential thermal analysis (DTA) can be conducted using thefollowing method. DTA runs can be made (using an instrument such as thatobtained from Netzsch Instruments, Selb, Germany, under the tradedesignation “NETZSCH STA 409 DTA/TGA”) using a −140+170 mesh sizefraction (i.e., the fraction collected between 105-micrometer openingsize and 90-micrometer opening size screens). An amount of each screenedsample (typically about 400 milligrams (mg)) is placed in a100-microliter Al₂O₃ sample holder. Each sample is heated in static airat a rate of 10° C./minute from room temperature (about 25° C.) to 1100°C.

[0141] Using powder x-ray diffraction, XRD, (using an x-raydiffractometer such as that obtained under the trade designation“PHILLIPS XRG 3100” from Phillips, Mahwah, N.J., with copper K_(α1)radiation of 1.54050 Angstrom) the phases present in a material can bedetermined by comparing the peaks present in the XRD trace of thecrystallized material to XRD patterns of crystalline phases provided inJCPDS (Joint Committee on Powder Diffraction Standards) databases,published by International Center for Diffraction Data. Furthermore, anXRD can be used qualitatively to determine types of phases. The presenceof a broad diffused intensity peak is taken as an indication of theamorphous nature of a material. The existence of both a broad peak andwell-defined peaks is taken as an indication of existence of crystallinematter within an amorphous matrix.

[0142] The initially formed amorphous material or ceramic (includingglass prior to crystallization) may be larger in size than that desired.The amorphous material or ceramic can be converted into smaller piecesusing crushing and/or comminuting techniques known in the art, includingroll crushing, canary milling, jaw crushing, hammer milling, ballmilling, jet milling, impact crushing, and the like. The shape of theceramic (including glass prior to crystallization) may depend, forexample, on the composition and/or microstructure of the ceramic, thegeometry in which it was cooled, and the manner in which the ceramic iscrushed (i.e., the crushing technique used). In general, where a“blocky” shape is preferred, more energy may be employed to achieve thisshape. Conversely, where a “sharp” shape is preferred, less energy maybe employed to achieve this shape. The crushing technique may also bechanged to achieve different desired shapes. The resulting particles mayhave an average aspect ratio ranging from 1:1 to 5:1, typically 1.25:1to 3:1, and preferably 1.5:1 to 2.5:1.

[0143] It is also within the scope of the present invention, forexample, to directly form ceramic (including glass prior tocrystallization) in desired shapes. For example, ceramic (includingglass prior to crystallization) may be formed (including molded) bypouring or forming the melt into a mold.

[0144] It is also within the scope of the present invention, forexample, to fabricate the ceramic (including glass prior tocrystallization) by coalescing. This coalescing step in essence forms alarger sized body from two or more smaller particles. For example,amorphous material comprising particles (obtained, for example, bycrushing) (including beads and microspheres), fibers, etc. may be formedinto an article. For example, ceramic (including glass prior tocrystallization), may also be provided by heating, for example,particles comprising the amorphous material, and/or fibers, etc. abovethe T_(g) such that the particles, etc. coalesce to form a shape andcooling the coalesced shape. The temperature and pressure used forcoalescing may depend, for example, upon composition of the amorphousmaterial and the desired density of the resulting material. Thetemperature should be desirably below glass crystallization temperature,and for glasses, greater than the glass transition temperature. In someembodiments, the temperature used in coalescing may exceed the glasscrystallization temperature. In certain embodiments, the heating isconducted at a temperature in a range of about 850° C. to about 1100° C.(in some embodiments, preferably 900° C. to 1000° C.). Typically, theamorphous material is under pressure (e.g., greater than zero to 1 GPaor more) during coalescence to aid the coalescence of the amorphousmaterial.

[0145] In one embodiment, a charge of the particles, etc. is placed intoa die and hot-pressing is performed at temperatures above glasstransition where viscous flow of glass leads to coalescence into arelatively large part. Examples of typical coalescing techniques includehot pressing, hot isostatic pressure, hot extrusion, and the like.During this coalescence step, articles of complex shapes can be obtainedby choosing suitable die constructions. Typically, it is generallypreferred to cool the resulting coalesced body before further heattreatment.

[0146] In another embodiment, a coalesced perform comprising glass isplaced into a die and is molded into useful shapes under the action ofheat and pressure such that the perform flows. The perform may be glassyor partially crystalline. The perform may have a range of densities offrom 50 to 100 of theoretical densities.

[0147] It is also within the scope of the present invention to conductadditional heat-treatment to further improve desirable properties of thematerial. For example, hot-isostatic pressing may be conducted (e.g., attemperatures from about 900° C. to about 1400° C.) to remove residualporosity, increasing the density of the material. Optionally, theresulting, coalesced article can be heat-treated to provideglass-ceramic, crystalline ceramic, or ceramic otherwise comprisingcrystalline ceramic.

[0148] Coalescence of the amorphous material and/or glass-ceramic (e.g.,particles) may also be accomplished by a variety of methods, includingpressureless or pressure sintering (e.g., sintering, plasma assistedsintering, hot pressing, HIPing, hot forging, hot extrusion, etc.).Coalescence of the amorphous material and/or glass-ceramic or shaping ofan already coalesced body may be accomplished with the use of suitabledental presses that can deliver the required temperature and heat. Oneembodiment of this process comprises the steps of forming a refractoryinvestment mold, inserting the material into the mold, heating, applyingpressure to the material such that it fills the mold cavity to form thedesired shape. An example of such a process is described in U.S. Pat.No. 6,465,106, incorporated by reference herein. A commercial example ofsuch a press is the Intra-Tech ProPress 100 (Whip-Mix Inc., Farmington,Ky.).

[0149] In another embodiment, the materials of this invention can beformed into mill blanks and machined to a desired shaped product. Themachining step can be accomplished in glassy, crystalline, orintermediate stages. Digitized CAD/CAM machining can be employed forthis task. Examples of such systems include CEREC (Sirona Dental SystemsGmbH, Bensheim, Germany) and Lava (3M Company, St. Paul, Minn.). It hasbeen surprisingly found that despite the high-strength nature of thematerial, it is quite machinable.

[0150] Heat-treatment can be carried out in any of a variety of ways,including those known in the art for heat-treating glass to provideglass-ceramics. For example, heat-treatment can be conducted in batches,for example, using resistive, inductively, or gas heated furnaces.Alternatively, for example, heat-treatment can be conductedcontinuously, for example, using a rotary kiln, fluidized bed furnace,or pendulum kiln. In the case of a rotary kiln or pendulum kiln, thematerial is fed directly into a kiln operating at the elevatedtemperature. The time at the elevated temperature may range from a fewseconds (in some embodiments even less than 5 seconds) to a few minutesto several hours. The temperature may range anywhere from the T_(x) ofthe amorphous material to 1600° C., from 900° C. to 1600° C., or between1200° C. to 1500° C.

[0151] The glass is heat-treated to at least partially crystallize theamorphous material to provide glass-ceramic. The heat-treatment ofcertain glasses to form glass-ceramics is well known in the art. Theheating conditions are generally carefully controlled to nucleate andgrow crystals to provide desired microstructure and properties. Oneskilled in the art can determine the appropriate conditions from aTime-Temperature-Transformation (TTT) study of the glass usingtechniques known in the art. One skilled in the art, after reading thedisclosure of the present invention should be able to provide TTT curvesfor glasses, determine the appropriate nucleation and/or crystal growthconditions to provide glass-ceramics.

[0152] In some embodiments of the present invention, the glasses orceramics comprising glass may be annealed prior to heat-treatment. Insuch cases, annealing is typically done at a temperature less than theT_(x) of the glass for a time from a few seconds to a few hours or evendays. Typically, the annealing is done for a period of less than 3hours, or even less than an hour. Optionally, annealing may also becarried out in atmospheres other than air.

[0153] Heat-treatment may occur, for example, by feeding the materialdirectly into a furnace at the elevated temperature. Alternatively, forexample, the material may be fed into a furnace at a much lowertemperature (e.g., room temperature) and then heated to desiredtemperature at a predetermined heating rate. It is within the scope ofthe present invention to conduct heat-treatment in an atmosphere otherthan air. In some cases it might be even desirable to heat-treat in areducing atmosphere(s). Also, for example, it may be desirable toheat-treat under gas pressure as in, for example, hot-isostatic press,or in gas pressure furnace. Although not wanting to be bound by theory,it is believed that the T_(g) and T_(x), as well as the T_(x)-T_(g) ofglasses according to the present application may shift depending uponthe atmospheres used during the heat treatment. It is also believed thatthe choice of atmospheres may affect oxidation states of some of thecomponents of the glasses and glass-ceramics. Such variation inoxidation state can bring about varying coloration of glasses andglass-ceramics. In addition, nucleation and crystallization steps can beaffected by atmospheres (e.g., the atmosphere may affect the atomicmobilities of some species of the glasses).

[0154] Typically, glass-ceramics are stronger than the amorphousmaterials from which they are formed. Hence, the strength of thematerial may be adjusted, for example, by the degree to which theamorphous material is converted to crystalline ceramic phase(s).Alternatively, or in addition, the strength of the material may also beaffected, for example, by the number of nucleation sites created, whichmay in turn be used to affect the number, and in turn the size of thecrystals of the crystalline phase(s). For additional details regardingforming glass-ceramics, see, for example Glass-Ceramics, P. W. McMillan,Academic Press, Inc., 2nd edition, 1979, the disclosure of which isincorporated herein by reference.

[0155] As compared to many other types of ceramic processing (e.g.,sintering of a calcined material to a dense, sintered ceramic material),there is relatively little shrinkage (typically, less than 30 percent byvolume; in some embodiments, less than 20 percent, 10 percent, 5percent, or even less than 3 percent by volume) during crystallizationof the glass to form the glass-ceramic. The actual amount of shrinkagedepends, for example, on the composition of the glass, theheat-treatment time, the heat-treatment temperature, the heat-treatmentpressure, the density of the glass being crystallized, the relativeamount(s) of the crystalline phases formed, and the degree ofcrystallization. The amount of shrinkage can be measured by conventionaltechniques known in the art, including by dilatometry, Archimedesmethod, or measuring the dimensions material before and afterheat-treatment. In cases, there may be some evolution of volatilespecies during heat-treatment.

[0156] For example, during heat-treatment of some exemplary amorphousmaterials containing ZrO₂ for making glass-ceramics according to presentinvention, formation of phases such as La₂Zr₂O₇, (Zr, M)O₂ solidsolution with face-centered cubic structure (where M=stabilizingcation), cubic/tetragonal ZrO₂, in some cases monoclinic ZrO₂, have beenobserved at temperatures above about 900° C. Although not wanting to bebound by theory, it is believed that zirconia-related phases are thefirst phases to nucleate from the amorphous material. In amorphousmaterials that do not contain ZrO₂ formation of Al₂O₃, ReAlO₃ (whereinRe is at least one rare earth cation), ReAl₁₁O₁₈, Re₃Al₅O₁₂, Y₃Al₅O₁₂,etc. phases takes place at temperatures above about 925° C. Typically,crystallite size during this nucleation step is on order of nanometers.For example, crystals as small as 10-15 nanometers have been observed.For at least some embodiments, heat-treatment at about 1300° C. forabout 1 hour provides a full crystallization. In general, heat-treatmenttimes for each of the nucleation and crystal growth steps may range of afew seconds (in some embodiments even less than 5 seconds) to severalminutes to an hour or more.

[0157] The size of the resulting crystals can typically be controlled atleast in part by the nucleation and/or crystallization times and/ortemperatures. Although it is generally preferred to have small crystals(e.g., on the order not greater than a micrometer, or even not greaterthan a nanometer), glass-ceramics may be made with larger crystal sizes(e.g., at least 1-10 micrometers, at least 10-25 micrometers, at least50-100 micrometers, or even grater than 100 micrometers). Although notwanting to be bound by theory, it is generally believed in the art thatthe finer the size of the crystals (for the same density), the higherthe mechanical properties (e.g., hardness and strength) of the ceramic.It is also within the scope of this invention to perform crystallizationin such a manner that crystals with needle, whisker or platelet-likemorphologies form during heat-treatment. Such crystals could favorablyaffect fracture toughness, machinability, and other characteristics ofthe resultant glass-ceramic.

[0158] Examples of crystalline phases which may be present inembodiments of glass-ceramics include: Al₂O₃ (e.g., (α-Al₂O₃, ortransitional Al₂O₃), Y₂O₃, REO, HfO₂, ZrO₂ (e.g., cubic ZrO₂ andtetragonal ZrO₂), BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO,NiO, Na₂O, P₂O₅, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, “complexmetal oxides” (including “complex Al₂03-metal oxide (e.g., complexAl₂O₃.REO (e.g., ReAlO₃ (e.g., GdAlO₃ LaAlO₃), ReAl₁₁O₁₈ (e.g.,LaAl11O₁₈,), and Re₃Al₅O₁₂ (e.g., Dy₃Al₅O₁₂)), complex Al₂O₃.Y₂O₃ (e.g.,Y₃Al₅O₁₂), and complex ZrO₂.REO (e.g., Re₂Zr₂O₇ (e.g., La₂Zr₂O₇))), andcombinations thereof.

[0159] It is also within the scope of the present invention tosubstitute a portion of the yttrium and/or aluminum cations in a complexAl₂O₃ metal oxide (e.g., complex Al₂O₃.Y₂O₃ (e.g., yttrium aluminateexhibiting a garnet crystal structure)) with other cations. For example,a portion of the Al cations in a complex Al₂O₃.Y₂O₃ may be substitutedwith at least one cation of an element selected from the groupconsisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinations thereof.For example, a portion of the Y cations in a complex Al₂O₃.Y₂O₃ may besubstituted with at least one cation of an element selected from thegroup consisting of: Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Th, Tm,Yb, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr, and combinations thereof.Similarly, it is also within the scope of the present invention tosubstitute a portion of the aluminum cations in alumina. For example,Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitute for aluminum in thealumina. The substitution of cations as described above may affect theproperties (e.g., hardness, toughness, strength, thermal conductivity,etc.) of the fused material.

[0160] It is also within the scope of the present invention tosubstitute a portion of the rare earth and/or aluminum cations in acomplex Al₂O₃.metal oxide (e.g., complex Al₂O₃.REO) with other cations.For example, a portion of the Al cations in a complex Al₂O₃.REO may besubstituted with at least one cation of an element selected from thegroup consisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinationsthereof. For example, a portion of the Y cations in a complex Al₂O₃.REOmay be substituted with at least one cation of an element selected fromthe group consisting of: Y, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr,and combinations thereof. Similarly, it is also within the scope of thepresent invention to substitute a portion of the aluminum cations inalumina. For example, Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitutefor aluminum in the alumina. The substitution of cations as describedabove may affect the properties (e.g., hardness, toughness, strength,thermal conductivity, etc.) of the fused material.

[0161] The average crystal size can be determined by the line interceptmethod according to the ASTM Standard E 112-96 “Standard Test Methodsfor Determining Average Grain Size”. The sample is mounted in mountingresin (such as that obtained under the trade designation “TRANSOPTICPOWDER” from Buehler Ltd., Lake Bluff, Ill.) typically in a cylinder ofresin about 2.5 cm in diameter and about 1.9 cm high. The mountedsection is prepared using conventional polishing techniques using apolisher (such as that obtained from Buehler Ltd., Lake Bluff, Ill.,under the trade designation “ECOMET 3”). The sample is polished forabout 3 minutes with a diamond wheel, followed by 5 minutes of polishingwith each of 45, 30, 15, 9, 3, and 1-micrometer slurries. The mountedand polished sample is sputtered with a thin layer of gold-palladium andviewed using a scanning electron microscopy (such as the JEOL SEM ModelJSM 840A). A typical back-scattered electron (BSE) micrograph of themicrostructure found in the sample is used to determine the averagecrystal size as follows. The number of crystals that intersect per unitlength (NL) of a random straight line drawn across the micrograph arecounted. The average crystal size is determined from this number usingthe following equation:${{Average}\quad {Crystal}\quad {Size}} = \frac{1.5}{N_{L}M}$

[0162] Where N_(L) is the number of crystals intersected per unit lengthand M is the magnification of the micrograph.

[0163] Some embodiments of the present invention include glass-ceramicscomprising crystals having at least one of an average crystal size notgreater than 150 nanometers.

[0164] Some embodiments of the present invention include glass-ceramicscomprising crystals, wherein at least 90 (in some embodimentspreferably, 95, or even 100) percent by number of the crystals presentin such portion have crystal sizes not greater than 200 nanometers.

[0165] Some embodiments of the present invention include glass-ceramicscomprising Al₂O₃, and a first complex Al₂O₃.Y₂O₃, and optionallycrystalline ZrO₂, and wherein at least one of the Al₂O₃, the optionalcrystalline ZrO₂, or the first complex Al₂O₃.Y₂O₃ has an average crystalsize not greater than 150 nanometers. In some embodiments preferably,the glass-ceramics further comprise a second, different complexAl₂O₃.Y₂O₃. In some embodiments preferably, the glass-ceramics furthercomprise a complex Al₂O₃.REO.

[0166] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.Y₂O₃, a second, different complexAl₂O₃.Y₂O₃, and optionally crystalline ZrO₂, and wherein for at leastone of the first complex Al₂O₃.Y₂O₃, the second complex Al₂O₃.Y₂O₃, orthe optional crystalline ZrO₂, at least 90 (in some embodimentspreferably, 95, or even 100) percent by number of the crystal sizesthereof are not greater than 200 nanometers. In some embodimentspreferably, the glass-ceramics further comprise a second, differentcomplex Al₂O₃.Y₂O₃. In some embodiments preferably, the glass-ceramicsfurther comprise a complex Al₂O₃.REO.

[0167] Some embodiments of the present invention include glass-ceramicscomprising Al₂O₃, a first complex Al₂O₃.REO, and optionally crystallineZrO₂, and wherein at least one of the Al₂O₃, the optional crystallineZrO₂, or the first complex Al₂O₃.REO has an average crystal size notgreater than 150 nanometers. In some embodiments preferably, theglass-ceramics further comprise a second, different complex Al₂O₃.REO.In some embodiments preferably, the glass-ceramics further comprise acomplex Al₂O₃.Y₂O₃.

[0168] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.REO, a second, different complexAl₂O₃.REO, and optionally crystalline ZrO₂, and wherein for at least oneof the first complex Al₂O₃.REO, the second complex Al₂O₃.REO, or theoptional crystalline ZrO₂, at least 90 (in some embodiments preferably,95, or even 100) percent by number of the crystal sizes thereof are notgreater than 200 nanometers. In some embodiments preferably, theglass-ceramics further comprise a complex Al₂O₃.Y₂O₃.

[0169] In some embodiments, glass-ceramics comprise at least 75, 80, 85,90, 95, 97, 98, 99, or even 100 percent by volume crystallites, whereinthe crystallites have an average size of less than 1 micrometer. In someembodiments, glass-ceramics comprise not greater than at least 75, 80,85, 90, 95, 97, 98, 99, or even 100 percent by volume crystallites,wherein the crystallites have an average size not greater than 0.5micrometer. In some embodiments, glass-ceramics comprise less than at75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystallites, wherein the crystallites have an average size not greaterthan 0.3 micrometer. In some embodiments, glass-ceramics comprise lessthan at least 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume crystallites, wherein the crystallites have an average size notgreater than 0.15 micrometer.

[0170] Crystals formed by heat-treating amorphous to provide embodimentsof glass-ceramics may be, for example, equiaxed, columnar, or flattenedsplat-like. The aspect ratio and overall size of whisker, needle, orplatelet-like crystals maybe optionally controlled to improveproperties.

[0171] Although a glass-ceramic may be in the form of a bulk material,it is also within the scope of the present invention to providecomposites comprising a glass-ceramic. Such a composite may comprise,for example, a phase or fibers (continuous or discontinuous) orparticles (including whiskers) (e.g., metal oxide particles, borideparticles, carbide particles, nitride particles, diamond particles,metallic particles, glass particles, and combinations thereof) dispersedin a glass-ceramic, invention or a layered-composite structure (e.g., agradient of glass-ceramic to amorphous material used to make theglass-ceramic and/or layers of different compositions ofglass-ceramics).

[0172] Typically, the (true) density, sometimes referred to as specificgravity, of ceramics is typically at least 70% of theoretical density.More desirably, the (true) density of ceramic is at least 75%, 80%, 85%,90%, 92%, 95%, 96%, 97%, 98%, 99%, 99.5%, or even 100% of theoreticaldensity.

[0173] The average hardness of the material of the present invention canbe determined as follows. Sections of the material are mounted inmounting resin (obtained under the trade designation “TRANSOPTIC POWDER”from Buehler Ltd., Lake Bluff, Ill.) typically in a cylinder of resinabout 2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler Ltd., Lake Bluff, Ill., under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The microhardness measurements aremade using a conventional microhardness tester (such as that obtainedunder the trade designation “MITUTOYO MVK-VL” from Mitutoyo Corporation,Tokyo, Japan) fitted with a Vickers indenter using a 100-gram indentload. The microhardness measurements are made according to theguidelines stated in ASTM Test Method E384 Test Methods forMicrohardness of Materials (1991), the disclosure of which isincorporated herein by reference.

[0174] Additional glasses and glass-ceramics, methods of making same,and methods of making articles containing same, which may be useful inthe articles and methods according to the present invention includethose disclosed in applications having U.S. application Ser. Nos.09/922,526, 09/922,527, 09/922,528, and 09/922,530, filed Aug. 2, 2001,now abandoned, Ser. Nos. 10/211,597, 10/211,638, 10/211,629, 10/211,598,10/211,630, 10/211,639, 10/211,034, 10/211,044, 10/211,628, 10/211,491,10/211,640, and 10/211,684, each filed Aug. 2, 2002, and Ser. No. ______(Attorney Case Nos. 58235US002, 58353US002, 58352US002, 58257US002, and58258US002), filed the same date as the instant application, thedisclosures of which are incorporated herein by reference.

[0175] Dental Materials

[0176] The ceramics, glass, and glass-ceramics described above can beincorporated into a hardenable resin to provide useful dental ororthodontic materials such as a paste. These resins are generallythermosetting materials capable of being hardened to form a polymernetwork including, for example, acrylate-functional materials,methacrylate-functional materials, epoxy-functional materials,vinyl-functional materials, and mixtures thereof. Suitably, thehardenable resin is made from one or more matrix-forming oligomer,monomer, polymer, or blend thereof.

[0177] Hardenable resins suitable for use in the dental materials of thepresent invention include hardenable organic materials having sufficientstrength, hydrolytic stability, and non-toxicity to render them suitablefor use in the oral environment. Examples of such materials includeacrylates, methacrylates, urethanes, carbamoylisocyanurates, epoxies(e.g., those shown in U.S. Pat. No. 3,066,112 (Bowen); U.S. Pat. No.3,539,533 (Lee II et al.); U.S. Pat. No. 3,629,187 (Waller); U.S. Pat.No. 3,709,866 (Waller); U.S. Pat. No. 3,751,399 (Lee et al.); U.S. Pat.No. 3,766,132 (Lee et al.); U.S. Pat. No. 3,860,556 (Taylor); U.S. Pat.No. 4,002,669 (Gross et al.); U.S. Pat. No. 4,115,346 (Gross et al.);U.S. Pat. No. 4,259,117 (Yamauchi et al.); U.S. Pat. No. 4,292,029(Craig et al.); U.S. Pat. No. 4,308,190 (Walkowiak et al.); U.S. Pat.No. 4,327,014 (Kawahara et al.); U.S. Pat. No. 4,379,695 (Orlowski etal.); U.S. Pat. No. 4,387,240 (Berg); U.S. Pat. No. 4,404,150 (Tsunekawaet al.)); and mixtures and derivatives thereof.

[0178] One class of preferred hardenable materials includes materialshaving free radically active functional groups. Examples of suchmaterials include monomers having one or more ethylenically unsaturatedgroup, oligomers having one or more ethylenically unsaturated group,polymers having one or more ethylenically unsaturated group, andcombinations thereof. Alternatively, the hardenable resin can beselected from materials that include cationically active functionalgroups. In another alternative, a mixture of hardenable resins thatinclude both cationically curable and free radically curable materialsmay be used for the dental materials of the invention. In anotheralternative, the hardenable resin can be a material from the class ofmaterials that includes both cationically active and free radicallyactive functional groups in the same molecule.

[0179] In the class of hardenable resins having free radically activefunctional groups, suitable materials for use in the invention containat least one ethylenically unsaturated bond, and are capable ofundergoing addition polymerization. Such free radically polymerizablematerials include mono-, di- or poly-acrylates and methacrylates such asmethyl acrylate, methyl methacrylate, ethyl acrylate, isopropylmethacrylate, n-hexyl acrylate, stearyl acrylate, allyl acrylate,glycerol diacrylate, glycerol triacrylate, ethyleneglycol diacrylate,diethyleneglycol diacrylate, triethyleneglycol dimethacrylate,1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate,trimethylolpropane triacrylate, 1,2,4-butanetriol trimethacrylate,1,4-cyclohexanediol diacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate,sorbitol hexacrylate, the diglycidyl methacrylate of bis-phenol A(“Bis-GMA”), bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, andtrishydroxyethyl-isocyanurate trimethacrylate; the bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight 200-500,copolymerizable mixtures of acrylated monomers such as those in U.S.Pat. No. 4,652,274 (Boettcher et al.), and acrylated oligomers such asthose of U.S. Pat. No. 4,642,126 (Zador); and vinyl compounds such asstyrene, diallyl phthalate, divinyl succinate, divinyl adipate anddivinylphthalate. Mixtures of two or more of these free radicallypolymerizable materials can be used if desired.

[0180] For free radical polymerization (e.g., hardening), an initiationsystem can be selected from systems that initiate polymerization viaradiation, heat, or redox/auto-cure chemical reaction. A class ofinitiators capable of initiating polymerization of free radically activefunctional groups includes free radical-generating photoinitiators,optionally combined with a photosensitizer or accelerator. Suchinitiators typically can be capable of generating free radicals foraddition polymerization upon exposure to light energy having awavelength between 200 and 800 nm.

[0181] A variety of visible or near-IR photoinitiator systems may beused for photopolymerization of free-radically polymerizable materials.For example, a photoinitiation system can be selected from systems whichinitiate polymerization via a two component system of an amine and anα-diketone as described in U.S. Pat. No. 4,071,424 (Dart et al.).Alternatively, the material can be combined with a three componentphotoinitiator system such as described in U.S. Pat. No. 5,545,676(Palazzotto et al.). The three component system includes an iodoniumsalt (e.g., a diaryliodonium salt), a sensitizer, and a donor. Eachphotoinitiator component is described in U.S. Pat. No. 5,545,676, column2, line 27, to column 4, line 45.

[0182] Other useful free-radical initiators include the class ofacylphosphine oxides, as described in European Pat. Application Publ.No. 173,567 (Ying) and U.S. Pat. No. 4,737,593 (Ellrich et al.) and U.S.Pat. No. 6,020,528 (Leppard et al.). Tertiary amine reducing agents maybe used in combination with an acylphosphine oxide.

[0183] Another free-radical initiator system that can alternatively beused in the dental materials of the invention includes the class ofionic dye-counterion complex initiators including a borate anion and acomplementary cationic dye. Borate salt photoinitiators are described,for example, in U.S. Pat. No. 4,772,530 (Gottschalk et al.); U.S. Pat.No. 4,954,414 (Adair et al.); U.S. Pat. No. 4,874,450 (Gottschalk); U.S.Pat. No. 5,055,372 (Shanklin et al.); and U.S. Pat. No. 5,057,393(Shanklin et al.).

[0184] Yet another alternative class of initiators capable of initiatingpolymerization of free radically active functional groups in thehardenable resin includes conventional chemical initiator systems suchas a combination of a peroxide and an amine. These initiators, whichrely upon a thermal redox reaction, are often referred to as “auto-curecatalysts.” They are typically supplied as two-part systems in which thereactants are stored apart from each other and then combined immediatelyprior to use.

[0185] In a further alternative, heat may be used to initiate thehardening, or polymerization, of free radically active groups. Examplesof heat sources suitable for the dental materials of the inventioninclude inductive, convective, and radiant. Thermal sources should becapable of generating temperatures of at least about 40° C. and at mostabout 150° C. under normal conditions or at elevated pressure. Thisprocedure is preferred for initiating polymerization of materialsoccurring outside of the oral environment.

[0186] Yet another alternative class of initiators capable of initiatingpolymerization of free radically active functional groups in thehardenable resin are those that include free radical-generating thermalinitiators. Examples include peroxides (e.g., benzoyl peroxide andlauryl peroxide) and azo compounds (e.g., 2,2-azobis-isobutyronitrile(AIBN)).

[0187] An alternative class of hardenable resins useful in dentalmaterials disclosed in the present application includes materials havingcationically active functional groups. Materials having cationicallyactive functional groups include cationically polymerizable epoxies,vinyl ethers, oxetanes, spiro-orthocarbonates, spiro-orthoesters, andthe like. Preferred materials having cationically active functionalgroups are epoxy-functional materials including, for example, thosedisclosed in U.S. Pat. No. 6,025,406 (Oxman et al.) (e.g., column 2,line 36, to column 4, line 52) and in the documents cited therein.

[0188] Optionally, monohydroxy- and polyhydroxy-alcohols may be added tothe hardenable resin, as chain-extenders for a hardenable resin havingcationically active functional groups, which are preferablyepoxy-functional materials. The hydroxyl-containing material used in thepresent invention can be any organic material having hydroxylfunctionality of at least about 1, and preferably at least about 2.Useful hydroxyl-containing materials are described, for example, in U.S.Pat. No. 5,856,373 (Kaisaki et al.).

[0189] For hardening resins including cationically active functionalgroups, an initiation system can be selected from systems that initiatepolymerization via radiation, heat, or redox/auto-cure chemicalreactions. For example, epoxy polymerization may be accomplished by theuse of thermal curing agents including, for example, anhydrides andamines. A particularly useful example of an anhydride curing agent iscis-1,2-cyclohexanedicarboxylic anhydride.

[0190] Alternatively, initiation systems for resins includingcationically active functional groups are those that are photoactivated.The broad class of cationic photoactive groups recognized in thecatalyst and photoinitiator industries may be used in the practice ofthe present invention. Photoactive cationic nuclei, photoactive cationicmoieties, and photoactive cationic organic compounds are art recognizedclasses of materials as exemplified by, for example, U.S. Pat. No.4,250,311 (Crivello); U.S. Pat. No. 3,708,296 (Schlesinger); U.S. Pat.No. 4,069,055 (Crivello); U.S. Pat. No. 4,216,288 (Crivello); U.S. Pat.No. 5,084,586 (Farooq); U.S. Pat. No. 5,124,417 (Farooq); U.S. Pat. No.4,985,340 (Palazzotto et al.); U.S. Pat. No. 5,089,536 (Palazzotto); andU.S. Pat. No. 5,856,373 (Kaisaki et al.).

[0191] The cationically-curable materials can be combined with a threecomponent or ternary photoinitiator system, as described above, forexample, using an iodonium salt, a sensitizer, and an electron donor.For hardening cationically curable materials, examples of usefularomatic iodonium complex salts are disclosed in U.S. Pat. No. 6,025,406(Oxman et al.) (e.g., column 5, line 46, to column 6, line 9). Examplesof useful sensitizers and electron donors can also be found in U.S. Pat.No. 6,025,406 (e.g., column 6, line 43, to column 9, line 43).

[0192] An alternative photoinitiator system for cationic polymerizationsincludes the use of organometallic complex cations essentially free ofmetal hydride or metal alkyl functionality selected from those describedin U.S. Pat. No. 4,985,340 (Palazzotto et al.).

[0193] Alternatively, the hardenable resins may have both cationicallyactive and free radically active functional groups contained in a singlemolecule. Such molecules may be obtained, for example, by reacting a di-or poly-epoxide with one or more equivalents of an ethylenicallyunsaturated carboxylic acid. An example of such a material is thereaction product of a material, which is available under the tradedesignation “UVR-6105” from Union Carbide, with one equivalent ofmethacrylic acid. Commercially available materials having epoxy andfree-radically active functionalities include materials available underthe trade designation “CYCLOMER” (e.g., “CYCLOMER M-100”, “M-101”, or“A-200”) from Daicel Chemical, Japan, and the material available underthe trade designation “EBECRYL-3605” from Radcure Specialties.

[0194] Photoinitiator compounds are preferably provided in dentalmaterials disclosed in the present application in an amount effective toinitiate or enhance the rate of cure or hardening of the resin system.Useful photopolymerizable compositions are prepared by simply admixing,under safe light conditions, the components as described above. Suitableinert solvents may be used, if desired, when preparing this mixture. Anysolvent that does not react appreciably with the components of theinventive compositions may be used. Examples of suitable solventsinclude, for example, acetone, dichloromethane, and acetonitrile. Aliquid material to be polymerized may be used as a solvent for anotherliquid or solid material to be polymerized. Solventless compositions canbe prepared, for example, by simply dissolving an aromatic iodoniumcomplex salt and sensitizer in an epoxy-functional material/polyolmixture with or without the use of mild heating to facilitatedissolution.

[0195] An additional class of hardenable resins include those withpendant acid moieties, which can undergo a setting reaction in thepresence of reactive fillers and water. Examples of suitable acidmoieties include carboxylates, phosphates, and phosphonates. Examples ofsuitable compounds include polyacrylic acid; polymers derived from theacrylic acid, methacrylic acid, itaconic acid, maleic acid, glutaconicacid, aconitic acid, citraconic acid, mesaconic acid, fumaric acid,tiglic acid, and combinations thereof; glycerol dimethacrylatephosphate; citric acid dimethacrylate; and propionic acid dimethacrylateand combinations thereof.

[0196] The dental materials of the invention may optionally includeadjuvants suitable for use in the oral environment including, forexample, colorants, flavorants, anti-microbials, fragrances,stabilizers, viscosity modifiers, and fluoride releasing materials. Forexample, a fluoride releasing glass may be added to dental materials orglasses of the present invention to provide the benefit of long-termrelease of fluoride in use, for example in the oral cavity.Fluoroaluminosilicate glasses are particularly preferred. Particularlypreferred fluoroaluminosilicate glasses are those that have been silanoltreated as described, for example, in U.S. Pat. No. 5,332,429 (Mitra etal.). Other suitable adjuvants include, for example, agents that impartfluorescence and/or opalescence.

[0197] Method of Making

[0198] In one embodiment of the present invention, dental or orthodonticmaterials are made by mixing a glass, glass-ceramic, or ceramic with ahardenable resin. The dental materials may be provided in variouscontainers including capsules, syringes, foli packages, and cartridges.Dental articles and orthodontic appliances may then be made by formingthe dental or orthodontic material into the desired shape and thenhardening the hardenable resin.

[0199] Typically, the dental material is initially a viscous material,for example, paste, and any of the standard methods for compoundingpaste may be used to form the composite material. Usually, methods whichoptimize mixing and minimize the incidence of material discontinuitiessuch as voids and cracks should be instituted. For example, applicationof vacuum or pressure can be beneficial during any stage of compounding,forming, or curing the paste. Pressure can be applied by various means,including isostatic, uniaxial, centrifugal, impact, or pressurized gas.Heat may optionally be applied at any stage. However, during curing, auniform temperature in the sample is preferably maintained to minimizeinternal stresses. During compounding and extrusion, methods thatminimize and preferably eliminate material discontinuities such as voidsor bubbles are preferred.

[0200] Mill blanks of dental or orthodontic material may be made in anydesired shape or size, including cylinders, bars, cubes, polyhedra,ovoids, and plates as is known in the art. Molds may be made of avariety of materials, including stainless steel, cobalt alloys, nickelalloys, aluminum alloys, plastic, glass, ceramic, or combinationsthereof. Alternatively, a variety of methods for forming and shaping theblanks into any desired configuration can be employed, such as injectionmolding, centrifugal casting and extrusion. During hardening,compression from springs or other means may optionally be used to reduceinternal stresses. Preferably, the outer surface of the blank is smoothand non-tacky.

[0201] Hardening may be performed in one or multiple stage methods. In atwo-stage process, it is preferred that initial hardening provide amaterial sufficient to sustain the forces of milling or carving. Thesecond hardening stage, therefore, can be performed on the compositeafter a dental article or orthodontic appliance is milled from a blankor molded. Such blanks are described in, for example, PCT PublicationNo. WO 01/13862 A1, incorporated by reference herein.

[0202] Hardened blocks may be attached to mounting stubs to facilitateaffixation of the blank in a milling machine. Mounting stubs function ashandles from which a blank is held by as it is milled by a machine.

[0203] Various means of milling the mill blanks of the present inventionmay be employed to create custom-fit dental prosthetics having a desiredshape and morphology. The term “milling” as used herein means abrading,polishing, controlled vaporization, electronic discharge milling (EDM),cutting by water jet or laser or any other method of cutting, removing,shaping, or carving material. While milling the blank by hand using ahand-held tool or instrument is possible, preferably the prosthetic ismilled by machine, including computer controlled milling equipment.However, a preferred device to create a prosthetic and achieve the fullbenefits of the composite material of the present invention is to use aCAD/CAM device capable of milling a blank, such as the Sirona Cerec 2machine. By using a CAD/CAM milling device, the prosthetic can befabricated efficiently and with precision. During milling, the contactarea may be dry, or it may be flushed with a lubricant. Alternatively,it may be flushed with an air or gas stream. Suitable lubricants arewell known in the art, and include water, oils, glycerine, ethyleneglycols, and silicones. After machine milling, some degree of finishing,polishing, and adjustment may be necessary to obtain a custom fit in tothe mouth and/or aesthetic appearance.

[0204] To fabricate blanks of the present invention, the following stepsare typically performed: Compound the paste; extrude the paste into amold; cure the paste via heat, light, microwave, e-beam or chemicalcure; remove the blank from its mold and trim excess if necessary; andoptionally, mount on a holder stub if necessary. An exemplary method ofmaking the dental mill blank of the present invention comprises thesteps of a) mixing a paste comprising a resin and a filler, b) shapingthe paste into a desired configuration, c) minimizing materialdiscontinuities from the paste, d) curing the paste into a blank, and e)relieving internal stresses in the blank.

[0205] Optionally, where a mold is used to shape the paste, excess pastematerial can be trimmed from the mold. The cured paste is then removedfrom the mold. Another optional step that can be performed in making amill blank is to mount a handle onto the cured paste. Preferably, thehandle is a holder stub.

[0206] Mill blanks of the present invention may be hardened in a mannersuch that the material contains minimal internal stresses. This may beaccomplished, for example, by application of pressure on the compositematerial during the hardening process. In the alternative, the avoidanceof internal stress imparted by shrinkage may be obtained by selection ofmill blank components such that the overall composition exhibits littleor no shrinkage during hardening. A preferred curing method entails theuse of light to fast harden the composite. During this fast hardening,the temperature may optionally be adjusted and controlled. The fasthardening technique requires a subsequent heat treatment to effectuatestress relief. Heat treatment of a hardened blank requires the blank beheated for a sufficient time and at a sufficient temperature toeffectively eliminate internal stresses such that the blank passes aThermal Shock Test. Preferably, the blank is raised to a temperature ofat or above T_(g) (glass transition temperature) of the resin componentof the blank. More preferably, the blank is heated to above T_(g) and ismaintained at that temperature for at least about one-half hour.

[0207] An exemplary method of heat treatment for a hardened blank is toplace the blank in an oven and raise the oven temperature to about theT_(g) of the resin component of the blank at a rate of about, forexample, 3-5° C./minute. Upon completing heat treatment, the blank isallowed to equilibrate to room temperature either by immersion into roomtemperature water or by slowly cooling via ambient temperature.Alternatively, the heat treatment may be accomplished by placing theblank in a preheated oven and maintaining the oven temperature at orabove T_(g) for a sufficient time to eliminate internal stresses in thecomposite blank.

[0208] Another method of curing the blanks of the present invention isthrough a slow hardening using low intensity light. In this technique,hardening is accomplished over a long period of time to minimizeinternal stresses, such that the resulting hardened blank will pass aThermal Shock Test. Preferably, the hardening takes place over a timeperiod of about 24 hours, however, it is envisioned that with properequipment and procedure, curing times may be shorter. Progress of thishardening may be evaluated by ascertaining a sample of the material atpredetermined times over the hardening time and evaluating progress ofhardening by Barcol Hardness measurement.

[0209] Other techniques may be used to relieve the stress of mill blanksof the present invention, including application of energy in a formother than heat, such as sonic or microwave energy.

[0210] The ceramics, glasses, and glass-ceramics described in thepresent application are useful in making dental articles and orthodonticappliances that comprise said ceramics, glasses, and glass-ceramics, asdescribed herein. The ceramics, glasses, and glass-ceramics describedherein may be formed, molded, shaped, pressed, etc. into the form ofdental articles and orthodontic appliances.

[0211] In one embodiment, a method of making a dental article ororthodontic appliance comprises the steps of optionally designing thedental article or the orthodontic appliance; carving a dental ororthodontic mill blank based on said optional design, wherein the dentalmill blank comprises a ceramic comprising at least one of the glasses orglass-ceramics described herein. The mill blank or the dental article ororthodontic appliance may be further heat treated as described herein.

[0212] In another embodiment, a method of making a dental article or anorthodontic appliance comprising the steps of designing the dentalarticle or the orthodontic appliance, heating a glass above the T_(g) ofthe glass such that the glass coalesce (or forms, in the case of aperform) to form a dental article or an orthodontic appliance having ashape based on said optional design; and cooling the coalesced article,wherein the glass comprises at least one of the glasses describedherein. The coalesced article may be further heat treated to form anarticle comprising glass-ceramic. The glass may be in the form ofparticles, powder, nanoclusters, fibers, flakes, whiskers, block, blank,beads, etc., or combinations thereof.

[0213] In another embodiment, a method of making a dental article ororthodontic appliance comprise the steps of optionally designing thedental article or the orthodontic appliance; combining a ceramic, glass,or glass-ceramic with a hardenable resin to form a mixture; forming thedental article or the orthodontic appliance into a shape based on saidoptional design; hardening said mixture to form the dental article ororthodontic appliance, wherein said ceramic comprises at least one ofthe glasses, or glass-ceramics described herein.

[0214] In another embodiment, the invention provides a method of makinga dental article or orthodontic appliance comprising the steps of plasmaor thermally spraying particles comprising metal oxide sources onto asuitable substrate such that the particles coalesce to form a shapedarticle and optionally separating the shaped article or appliance fromthe substrate, wherein the shaped article comprises at least one of theglasses described herein. Useful substrates include refractory materialsthat comprise admixtures of silica, silicon carbide, magnesium oxide,mono ammonium phosphate, zircon or aluminum oxide. Metal substrates canalso be used in some embodiments.

[0215] Uses

[0216] The dental materials, glasses, ceramics, and glass-ceramicsdisclosed in the present application can be used, for example, as dentaladhesives, artificial crowns, anterior or posterior fillings, castingmaterials, cavity liners, pastes, cements, coating compositions, millblanks, orthodontic appliances, dental articles, restoratives,prostheses, and sealants. For example, restoratives of the invention canbe placed directly in the mouth, shaped or formed, and cured (hardened)in-situ, or alternatively, may be fabricated into a prosthesis outsidethe mouth and subsequently adhered in place inside the mouth.

[0217] Practitioners generally desire handling properties in a dentalmaterial that allows fast and easy placement, which often translates totime savings. For example, in dental restorative work, it is desirablein some instances that dental materials do not slump (e.g., flow orchange in shape), because after a practitioner places the material inthe mouth and manipulates the material by contouring and feathering, thepractitioner generally wants the imparted shape to remain unchangeduntil the material is hardened. Materials used for restorative work,having a sufficiently high yield stress generally will not slump; thatis, they will not flow under the stress of gravity. The yield stress ofa material is the minimum stress required to cause the material to flow,and is described in “Rheology Principles, Measurements, andApplications” by C. W. Macosko, VCH Publishers, Inc., New York, 1994, p.92. If the stress due to gravity is below the yield stress of thematerial, then the material will not flow. The stress due to gravity,however, will depend on the mass of dental material being placed as wellas the shape.

[0218] “Contouring” refers to the process of shaping a material (usingdental instruments) so that it resembles the natural dental anatomy. Foreasy contouring, materials should have a sufficiently high viscositythat they maintain their shape after manipulation with a dentalinstrument, and yet the viscosity should not be so high that it isdifficult to shape the material. “Feathering” refers to the process ofreducing the dental material to a thin film in order to blend thematerial into the natural dentition. This is done with a dentalinstrument at the margin of the manipulated material and the naturaldentition. It is also desirable that the dental material not stick toplacement instruments, to minimize further alteration of the shape orsurface topography.

[0219] In an embodiment where the dental material of the invention is arestorative, the dental material preferably has little to no slump, yeteasily adapts to, for example, a cavity preparation, and is easilycontoured and feathered. Preferably, the dental materials of theinvention do not stick to placement instruments, and are advantageously,overall, fast and easy to use in dental procedures such as, for example,restoring tooth structure.

[0220] In certain embodiments, the present invention provides dentalmaterials that are capable of being hardened to provide a balance ofdesirable properties as detailed below (e.g., a low opacity, a lowvolumetric shrinkage value, a high diametral tensile strength, a highcompressive strength, a high retention of gloss upon polishing).

[0221] The dental materials of the present invention may be hardened toform, for example, dental articles and orthodontic appliances. In amethod of using dental materials including a hardenable resin andceramics as disclosed in the present application, the dental materialmay be placed near or on a tooth surface, followed by a manipulation bythe practitioner or laboratory to change the topography of the material,then the resin may be hardened. These steps can be followed sequentiallyor in a different order. For example, where the dental material is amill blank or an article or appliance, the hardening step is generallycompleted prior to changing the topography of the dental material.Changing the topography of the dental material can be accomplished invarious ways including, for example, carving or manual manipulationusing hand held instruments, or by machine or computer aided apparatus(e.g., a CAD/CAM milling machine) in the case of prostheses and millblanks. Optionally, a finishing step can be performed to polish, finish,or apply a coating on the dental article.

[0222] A dental article or orthodontic appliance can be attached to thetooth or bone structure with conventional cements or adhesives or otherappropriate means such as glass ionomer, resin cement, zinc phosphate,zinc polycarboxylate, compomer, or resin-modified glass. In addition,material can optionally be added to the milled article or appliance forvarious purposes including repair, correction, or enhancing esthetics.The additional material may be of one or more different shades orcolors. The added material may be composite, ceramic, or metal. A dentalporcelain or light-cured composite is preferred.

[0223] Strength can be characterized by mechanical measurements such ascompressive strength (CS) and diametral tensile strength (DTS). Highcompressive strength in a dental material is advantageous due to theforces exerted by mastication on dental repairs, replacements, andrestorations. Some embodiments of the dental articles and orthodonticappliances disclosed in the present application may exhibit desirableaesthetic qualities including high translucency, high gloss, and highretention of polish after exposure to repetitive abrasion.

[0224] Aesthetic quality of a dental article or orthodontic appliance,although a somewhat subjective characteristic (yet well-understood inthe dental industry), can be preferably quantified in one aspect, bymeasuring MacBeth values, in which lower MacBeth values indicate a lowervisual opacity. Visual opacity is indicative of dental article's ororthodontic appliance's level of translucency. Low visual opacity isdesired so that the hardened dental material will have a life-likeluster.

[0225] High translucency of a dental article or orthodontic appliancecontributes to the aesthetic character and quality of the material.Polishability of such articles and appliances also contributes to theaesthetic character and quality of the material. The ability of sucharticles and appliances to have a glossy finish and life-like lusterupon polishing is highly desirable. An even greater benefit is theability of such articles and appliances to retain their luster evenafter repetitive abrasive contact, such as tooth brushing. It has beensurprisingly found that some embodiments of dental articles andorthodontic appliances disclosed in the present application have highpolishability and are able to retain the polish and luster afterrepetitive tooth brushing.

[0226] The dental materials, dental articles, and orthodontic appliancesof the invention can be incorporated into kits, wherein at least one ofthe articles or appliances is a dental material, dental article ororthodontic appliance of the invention. The kits may also include one ormore other components such as a dental mill blank, a bonding agent, amilling lubricant, a color-matching composition suitable for using in anoral environment, an impression material, an instrument, a dentalcomposite, a paste, a dental porcelain, an abrasive, an orthodonticadhesive, an adhesive primer, an appliance positioning tool,instructions for the use of any of these components alone or incombination with any other component or components, and combinationsthereof.

[0227] Other uses of the ceramics, glasses, and glass-ceramics describedherein are as reactive fillers for use in glass ionomers cement asdescribed in U.S. Pat. No. 6,136,885, PCT Publication No. WO 02/085313,and U.S. Pat. No. 5,130,347, incorporated by reference herein; asmaterials for dental restorations applied by flame spraying as describedin U.S. Pat. No. 6,938,990 B1, incorporated by reference herein; in theforming methods described in U.S. Pat. No. 6,342,458 B1, incorporated byreference herein; as dental mill blanks as described in U.S. Pat. No.6,394,880, incorporated by reference herein; as a porous material forglass infiltration as described in U.S. Pat. Nos. 5,910,273 and5,250,352, incorporated by reference herein.

EXAMPLES

[0228] Raw materials used to make the amorphous glass beads in theExamples were obtained from the following sources unless otherwiseindicated Raw Material Source Alumina powder Obtained from Condea Vista,Tucson, AZ, (Al₂O₃) under the trade designation “APA-0.5” Calcium oxideObtained from Alfa Aesar, Ward Hill, MA powder (CaO) Calcium fluorideObtained from Alfa Aesar powder (CaF₂) Cerium oxide Obtained fromRhone-Poulenc, France powder (CeO₂) Chromium oxide Obtained from AldrichChemical Company, powder (Cr₂O₃) Milwaukee, WI Dysprosium oxide Obtainedfrom Aldrich Chemical Company powder (Dy₂O₃) Erbium oxide Obtained fromAldrich Chemical Company powder (Er₂O₃) Europium oxide Obtained fromAldrich Chemical Company powder (Eu₂O₃) Gadolinium oxide Obtained fromMolycorp Inc., Mountain Pass, powder (Gd₂O₃) CA Hafnium oxide Obtainedfrom Teledyne Wah Chang Albany powder (HfO₂) Company, Albany, OR Ironoxide Obtained from Aldrich Chemical Company powder (Fe₂O₃) Lanthanumoxide Obtained from Molycorp Inc. powder (La₂O₃) Lithium carbonateObtained from Aldrich Chemical Company powder (Li₂CO₃) Magnesium oxideObtained from Aldrich Chemical Company powder (MgO) Manganese oxideObtained from Aldrich Chemical Company powder (MNO) Neodymium oxideObtained from Molycorp Inc. Niobium oxide Obtained from Aldrich ChemicalCompany powder (Nb₂O₅) Phosphorous oxide Obtained from Aldrich ChemicalCompany powder (P₂O₅) Silica powder Obtained from Alfa Aesar (SiO₂)Sodium bicarbonate Obtained from Aldrich Chemical Company powder(NaHCO₃) Strontium oxide Obtained from Alfa Aesar powder (SrO) Tantalumoxide Obtained from Aldrich Chemical Company powder (Ta₂O₅) Titaniumdioxide Obtained from Kemira Inc., Savannah, GA powder (TiO₂) Yttriumoxide Obtained from H.C. Stark, Newton, MA powder (Y₂O₃)Yttria-stabilized Obtained from Zirconia Sales, Inc., Marietta,zirconium oxide powder (Y-PSZ) GA, under the trade designation “HSY-3”

[0229] Description, source, and abbreviations for the materials used tomake the photocurable resins described in these Examples. AbbreviationDescription Source Bis-GMA 2,2-Bis[4-(2-hydroxy-3- Made according tomethacryloyloxy-propoxy) generally accepted phenyl]propane proceduresknown in the (CAS No. 1565-94-2) art UDMA Diurethane Dimethacrylate RohmTech, Inc., (CAS No. 41137-60-4), Malden, MA commercially available as“ROHAMERE6661-0” Bis-EMA6 Ethoxylated (6 mole Sartomer Co., ethyleneoxide) Bisphenol Exton, PA A Dimethacrylate (CAS No. 41637-38-1),commercially available as “Sartomer CD541” TEGDMA TriethyleneglycolSartomer Co. Dimethacrylate CPQ Camphorquinone Sigma-Aldrich, St. Louis,MO DPIHFP Diphenyl Iodonium Johnson Matthey, Alpha HexafluorophosphateAesar Division, Ward Hill, NJ EDMAB Ethyl 4-DimethylaminobenzoateSigma-Aldrich BHT 2,6-Di-tert-butyl-4-methylphenol Sigma-Aldrich NORBLOC2-(2′-Hydroxy-5′- Janssen 7966 methacryloxyethylphenyl)-H- benzotriazole(CAS No. Pharmaceuticals, 96478-09-0) Titusville, PA HEMA 2-HydroxethylMethacrylate DeGussa Corp./Rohm America Inc.

Example 1

[0230] A polyurethane-lined mill was charged with 819.6 grams (g) ofalumina particles (“APA-0.5”), 818 g of lanthanum oxide particles(obtained from Molycorp, Inc.), 362.4 g of yttria-stabilized zirconiumoxide particles (with a nominal composition of 94.6 wt-% ZrO₂ (+HfO₂)and 5.4 wt-% Y₂O₃ (obtained under the trade designation “HSY-3” fromZirconia Sales, Inc. of Marietta, Ga.), 1050 g of distilled water andabout 2000 g of zirconia milling media (obtained from Tosoh Ceramics,Division of Bound Brook, N.J., under the trade designation “YTZ”). Themixture was milled at 120 revolutions per minute (rpm) for 4 hours tothoroughly mix the ingredients. After the milling, the milling mediawere removed and the slurry was poured onto a glass (“PYREX”) pan whereit was dried using a heat-gun. The dried mixture was ground with amortar and pestle and screened through a 70-mesh screen (212-micrometeropening size). After grinding and screening, some of the particles werefed into a hydrogen/oxygen torch flame. The hydrogen torch used to meltthe multiphase particles, thereby generating a melted amorphous glassbead, was a Bethlehem bench burner, delivering hydrogen and oxygen atthe following rates. For the inner ring, the hydrogen flow rate was 8standard liters per minute (SLPM), the oxygen flow rate was 3 SLPM. Forthe outer ring, the hydrogen flow rate was 23 standard liters per minute(SLPM), the oxygen flow rate was 9.8 SLPM. The dried and sized particleswere fed directly into the hydrogen torch flame, where they were meltedand transported to an inclined stainless steel surface (approximately 20inches wide with the slope angle of 45 degrees) with cold water runningover (approximately 2 L/min). Obtained in this procedure amorphous beadsranged in size from 30 to 150 microns.

[0231] About 50 g of the amorphous beads was placed in a graphite dieand hot-pressed using a uniaxial pressing apparatus (obtained under thetrade designation “HP-50”, Thermal Technology Inc., Brea, Calif.). Thehot-pressing was carried out at 960° C. in an argon atmosphere and 13.8megapascals (MPa) (2000 pounds per square inch (2 ksi)) pressure. Theresulting disk was about 48 millimeters in diameter, and about 5 mmthick. Additional hot-press runs were performed to make additionaldisks. FIG. 1 is an optical photomicrograph of a sectioned bar (2-mmthick) of the hot-pressed material demonstrating its transparency.

[0232] The Young's Modulus (E) of the resulting hot-pressed glassmaterial was measured using a ultrasonic test system (obtained fromNortek, Richland, Wash., under the trade designation “NDT-140”), andfound to be within a range of about 130-150 GPa.

[0233] The average microhardnesses of the resulting hot-pressed materialwas determined as follows. Pieces of the hot-pressed material (about 2to 5 millimiters in size) were mounted in mounting resin (obtained underthe trade designation “EPOMET” from Buehler Ltd., Lake Bluff, Ill.). Theresulting cylinder of resin was about 2.5 cm (1 inch) in diameter andabout 1.9 cm (0.75 inch) tall (i.e., high). The mounted samples werepolished using a conventional grinder/polisher (obtained under the tradedesignation “EPOMET” from Buehler Ltd.) and conventional diamondslurries with the final polishing step using a 1-micrometer diamondslurry (obtained under the trade designation “METADI” from Buehler Ltd.)to obtain polished cross-sections of the sample.

[0234] The microhardness measurements were made using a conventionalmicrohardness tester (obtained under the trade designation “MITUTOYOMVK-VL” from Mitutoyo Corporation, Tokyo, Japan) fitted with a Vickersindenter using a 500-gram indent load. The microhardness measurementswere made according to the guidelines stated in ASTM Test Method E384Test Methods for Microhardness of Materials' (1991), the disclosure ofwhich is incorporated herein by reference. The microhardness values werean average of 20 measurements. The average microhardness of thehot-pressed material was about 8.3 GPa.

[0235] The average indentation toughness of the hot-pressed material wascalculated by measuring the crack lengths extending from the apices ofthe vickers indents made using a 500 g load with a microhardness tester(obtained under the trade designation “MITUTOYO MVK-VL” from MitutoyoCorporation, Tokyo, Japan). Indentation toughness (K_(IC)) wascalculated according to the equation:

K _(IC)=0.016 (E/H)^(1/2)(P/c)^(3/2)

[0236] wherein:

[0237] E=Young's Modulus of the material;

[0238] H=Vickers hardness;

[0239] P=Newtons of force on the indenter;

[0240] c=Length of the crack from the center of the indent to its end.

[0241] Samples for the toughness were prepared as described above forthe microhardness test. The reported indentation toughness values are anaverage of 5 measurements. Crack (c) were measured with a digitalcaliper on photomicrographs taken using a scanning electron microscope(“JEOL SEM” (Model JSM 6400)). The average indentation toughness of thehot-pressed material was 1.4 MPa·m^(1/2).

[0242] The thermal expansion coefficient of the hot-pressed material wasmeasured using a thermal analyser (obtained from Perkin Elmer, Shelton,Conn., under the trade designation “PERKIN ELMER THERMAL ANALYSER”). Theaverage thermal expansion coefficient was 7.6×10⁻⁶/° C.

[0243] The thermal conductivity of the hot-pressed material was measuredaccording to an ASTM Standard “D 5470-95, Test Method A” (1995), thedisclosure of which is incorporated herein by reference. The averagethermal conductivity was 1.15 W/m·K.

[0244] The translucent disk of hot-pressed La₂O₃—Al₂O₃—ZrO₂ glass washeat-treated in a furnace (an electrically heated furnace (obtainedunder the trade designation “Model KKSK-666-3100” from Keith Furnaces ofPico Rivera, Calif.)) as follows. The disk was first heated from roomtemperature (about 25° C.) to about 900° C. at a rate of about 10°C./min and then held at 900° C. for about 1 hour. Next, the disk washeated from about 900° C. to about 1300° C. at a rate of about 10°C./min and then held at 1300° C. for about 1 hour, before cooling backto room temperature by turning off the furnace. Additional run wasperformed as described above except the final temperature was 1400° C.

[0245]FIG. 2(a,b) is a scanning electron microscope (SEM)photomicrograph of a polished section of Example 1 materialsheat-treated at 1300° C. and 1400° C., respectively, showing the finecrystalline nature of the material and the influence of the processingconditions on the crystallinity of the product. The polished section wasprepared using conventional mounting and polishing techniques.

[0246] Based on powder x-ray diffraction of a portion of heat-treatedExample 1 material and examination of the polished sample using SEM inthe backscattered mode, it is believed that the dark portions in thephotomicrograph were crystalline LaAl₁₁O₁₈, the gray portionscrystalline LaAlO₃, and the white portions crystalline cubic/tetragonalZrO₂. The Young's Modulus (E) of the heat-treated material was measuredusing an ultrasonic test system (obtained from Nortek, Richland, Wash.,under the trade designation “NDT-140”), and found to be about 260 GPa.The average microhardness of the heat-treated at 1300° C. material wasdetermined as described above was found to be 18.3 GPa. The averagefracture toughness (K_(Ic)) of the heat-treated at 1300° C. material wasdetermined as described above and was found to be 3.4 Mpa.m^(1/2).

[0247] The average microhardness of the heat-treated at 1400° C.material was determined to be 15.4 GPa. The average fracture toughness(K_(Ic)) of the heat-treated at 1400° C. material was determined to be5.7 Mpa·m^(1/2).

[0248] The crush strength was measured for 90-125 micron amorphous beadsaccording to the test procedure described in U.S. Pat. No. 4,772,511(Wood et al.). (See Table I for crystallization conditions.) Forcomparison purposes, the crush strength of YTZ (yttria tetragonalzirconia) crystalline beads (100 microns in size) obtained from TosohCeramics was also measured. Table I demonstrates the superior strengthof beaded glass-ceramic materials of this invention compared to ZrO₂.TABLE I Crush Strength of Beaded Glass- ceramic Materials of theInvention Material Heat-treatment, ° C. Appearance Crush-strength, MPaExample 1 1225 Hazy/Clear 1601 Example 1 1300 Opaque 2282 ZrO₂ (“YTZ”)None Opaque 1234

Examples 2-62

[0249] Examples 2-62 beads were prepared as described in Example 1,except the raw materials and the amounts used are listed in Table II,below, and milling of raw materials was carried out in 90 ml ofisopropyl alcohol with 200 g of the zirconia media (obtained from TosohCeramics, Division of Bound Brook, N.J., under “YTZ” designation) at 120rpm for 24 hours. TABLE II Bead Formulations Weight Percent of ExampleComponents Powder Batch Amounts, g 2 La₂O₃: 45.06 La₂O₃: 22.53 Al₂O₃:34.98 Al₂O₃: 17.49 ZrO₂: 19.96 ZrO₂: 9.98 3 La₂O₃: 42.29 La₂O₃: 21.15Al₂O₃: 38.98 Al₂O₃: 19.49 ZrO₂: 8.73 ZrO₂: 9.37 4 La₂O₃: 39.51 La₂O₃:19.76 Al₂O₃: 42.98 Al₂O₃: 21.49 ZrO₂: 17.51 ZrO₂: 8.76 5 La₂O₃: 36.74La₂O₃: 18.37 Al₂O₃: 46.98 Al₂O₃: 23.49 ZrO₂: 16.28 ZrO₂: 8.14 6 La₂O₃:38.65 La₂O₃: 19.33 Al₂O₃: 38.73 Al₂O₃: 19.37 ZrO₂: 22.62 ZrO₂: 11.31 7La₂O₃: 40.15 La₂O₃: 20.08 Al₂O₃: 40.23 Al₂O₃: 20.12 ZrO₂: 19.62 ZrO₂:9.81 8 La₂O₃: 43.15 La₂O₃: 21.58 Al₂O₃: 43.23 Al₂O₃: 21.62 ZrO₂: 13.62ZrO₂: 6.81 9 La₂O₃: 35.35 La₂O₃: 17.68 Al₂O₃: 48.98 Al₂O₃: 24.49 ZrO₂:15.66 ZrO₂: 7.83 10 La₂O₃: 32.58 La₂O₃: 16.20 Al₂O₃: 52.98 Al₂O₃: 26.49ZrO₂: 14.44 ZrO₂: 7.22 11 La₂O₃: 31.20 La₂O₃: 15.60 Al₂O₃: 54.98 Al₂O₃:27.49 ZrO₂: 13.82 ZrO₂: 6.91 12 La₂O₃: 28.43 La₂O₃: 14.22 Al₂O₃: 58.98Al₂O₃: 29.49 ZrO₂: 12.59 ZrO₂: 6.30 13 La₂O₃: 26.67 La₂O₃: 13.34 Al₂O₃:55.33 Al₂O₃: 27.67 ZrO₂: 18.00 ZrO₂: 9.00 14 ZrO₂: 5.00 ZrO₂: 2.50La₂O₃: 86.50 La₂O₃: 43.25 Al₂O₃: 8.50 Al₂O₃: 4.25 15 ZrO₂: 10.00 ZrO₂:5.00 La₂O₃: 81.90 La₂O₃: 40.95 Al₂O₃: 8.10 Al₂O₃: 4.05 16 CeO₂: 41.40CeO₂: 20.70 Al₂O₃: 40.60 Al₂O₃: 20.30 ZrO₂: 18.00 ZrO₂: 9.00 17 Al₂O₃:41.00 Al₂O₃: 20.50 ZrO₂: 17.00 ZrO₂: 8.50 Eu₂O₃: 41.00 Eu₂O₃: 20.50 18Al₂O₃: 41.00 Al₂O₃: 20.50 ZrO₂: 18.00 ZrO₂: 9.00 Gd₂O₃: 41.00 Gd₂O₃:20.50 19 Al₂O₃: 41.00 Al₂O₃: 20.50 ZrO₂: 18.00 ZrO₂: 9.00 Dy₂O₃: 41.00Dy₂O₃: 20.50 20 Al₂O₃: 40.90 Al₂O₃: 20.45 Er₂O₃: 40.90 Er₂O₃: 20.45ZrO₂: 18.20 ZrO₂: 9.10 21 La₂O₃: 35.00 La₂O₃: 17.50 Al₂O₃: 40.98 Al₂O₃:20.49 ZrO₂: 18.12 ZrO₂: 9.06 Nd₂O₃: 5.00 Nd₂O₃: 2.50 22 La₂O₃: 35.00La₂O₃: 17.50 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂: 18.12 ZrO₂: 9.06 CeO₂: 5.00CeO₂: 2.50 23 La₂O₃: 35.00 La₂O₃: 17.50 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂:18.12 ZrO₂: 9.06 Eu₂O₃: 5.00 Eu₂O₃: 2.50 24 La₂O₃: 35.00 La₂O₃: 17.50Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂: 18.12 ZrO₂: 9.06 Er₂O₃: 5.00 Er₂O₃: 2.5025 HfO₂: 35.50 HfO₂: 17.75 Al₂O₃: 32.50 Al₂O₃: 16.25 La₂O₃: 32.50 La₂O₃:16.25 26 La₂O₃: 41.7 La₂O₃: 20.85 Al₂O₃: 35.4 Al₂O₃: 17.70 ZrO₂: 16.9ZrO₂: 8.45 MgO: 6.0 MgO: 3.00 27 La₂O₃: 39.90 La₂O₃: 19.95 Al₂O₃: 33.90Al₂O₃: 16.95 ZrO₂: 16.20 ZrO₂: 8.10 MgO: 10.00 MgO: 5.00 28 La₂O₃: 43.02La₂O₃: 21.51 Al₂O₃: 36.50 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 Li₂CO₃:3.00 Li₂CO₃: 1.50 29 La₂O₃: 41.70 La₂O₃: 20.85 Al₂O₃: 35.40 Al₂O₃: 17.70ZrO₂: 16.90 ZrO₂: 8.45 Li₂CO₃: 6.00 Li₂CO₃: 3.00 30 La₂O₃: 38.80 La₂O₃:19.40 Al₂O₃: 40.70 Al₂O₃: 20.35 ZrO₂: 17.50 ZrO₂: 8.75 Li₂CO₃: 3.00Li₂CO₃: 1.50 31 La₂O₃: 43.02 La₂O₃: 21.51 Al₂O₃: 36.50 Al₂O₃: 18.25ZrO₂: 17.46 ZrO₂: 8.73 TiO₂: 3.00 TiO₂: 1.50 32 La₂O₃: 43.02 La₂O₃:21.51 Al₂O₃: 36.50 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 NaHCO₃: 3.0NaHCO₃: 1.50 33 La₂O₃: 42.36 La₂O₃: 21.18 Al₂O₃: 35.94 Al₂O₃: 17.97ZrO₂: 17.20 ZrO₂: 8.60 NaHCO₃: 4.50 NaHCO₃: 2.25 34 La₂O₃: 43.02 La₂O₃:21.51 Al₂O₃: 36.50 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 MgO: 1.50 MgO:0.75 NaHCO₃: 1.50 NaHCO₃: 0.75 TiO₂: 1.50 TiO₂: 0.75 35 La₂O₃: 43.00La₂O₃: 21.50 Al₂O₃: 32.00 Al₂O₃: 16.0 ZrO₂: 12.00 ZrO₂: 6.00 SiO₂: 13.00SiO₂: 6.50 36 Y₂O₃: 28.08 Y₂O₃: 14.04 Al₂O₃: 58.48 Al₂O₃: 29.24 ZrO₂:13.44 ZrO₂: 6.72 37 Y₂O₃: 27.6 Y₂O₃: 13.80 Al₂O₃: 57.50 Al₂O₃: 23.75ZrO₂: 14.90 ZrO₂: 7.45 38 Y₂O₃: 27.44 Y₂O₃: 13.72 Al₂O₃: 57.14 Al₂O₃:28.57 ZrO₂: 15.43 ZrO₂: 7.71 39 Y₂O₃: 28.70 Y₂O₃: 14.35 Al₂O₃: 55.70Al₂O₃: 27.85 ZrO₂: 15.50 ZrO₂: 7.75 40 Y₂O₃: 19.00 Y₂O₃: 9.50 Al₂O₃:51.00 Al₂O₃: 25.50 ZrO₂: 17.90 ZrO₂: 8.95 La₂O₃: 12.10 La₂O₃: 6.05 41Y₂O₃: 19.30 Y₂O₃: 9.65 Al₂O₃: 50.50 Al₂O₃: 25.25 ZrO₂: 17.80 ZrO₂: 8.90Nd₂O₃: 12.40 Nd₂O₃: 6.20 42 Y₂O₃: 19.10 Y₂O₃: 9.55 Al₂O₃: 50 Al₂O₃:25.00 ZrO₂: 17.80 ZrO₂: 8.90 Gd₂O₃: 13.10 Gd₂O₃: 6.55 43 Y₂O₃: 19.00Y₂O₃: 9.50 Al₂O₃: 49.70 Al₂O₃: 24.85 ZrO₂: 17.55 ZrO₂: 8.77 Er₂O₃: 13.80Er₂O₃: 6.90 44 Y₂O₃: 27.40 Y₂O₃: 13.70 Al₂O₃: 50.30 Al₂O₃: 25.15 ZrO₂:17.80 ZrO₂: 8.90 Li₂CO₃: 4.50 Li₂CO₃: 2.25 45 HfO₂: 20.08 HfO₂: 14.04Al₂O₃: 46.55 Al₂O₃: 23.27 Y₂O₃: 25.37 Y₂O₃: 12.67 46 Y₂O₃: 27.40 Y₂O₃:13.7 Al₂O₃: 50.30 Al₂O₃: 25.15 ZrO₂: 17.80 ZrO₂: 8.90 MgO: 4.50 MgO:2.25 47 Y₂O₃: 27.40 Y₂O₃: 13.70 Al₂O₃: 50.30 Al₂O₃: 25.15 ZrO₂: 17.80ZrO₂: 8.90 CaO: 4.50 CaO: 2.25 48 Y₂O₃: 27.40 Y₂O₃: 13.70 Al₂O₃: 50.30Al₂O₃: 25.15 ZrO₂: 17.80 ZrO₂: 8.90 TiO₂: 4.50 TiO₂: 2.25 49 Y₂O₃: 27.40Y₂O₃: 13.70 Al₂O₃: 50.30 Al₂O₃: 25.15 ZrO₂: 17.80 ZrO₂: 8.90 NaHCO₃:4.50 NaHCO₃: 2.25 50 Y₂O₃: 27.40 Y₂O₃: 13.70 Al₂O₃: 50.30 Al₂O₃: 25.15ZrO₂: 17.80 ZrO₂: 8.90 SiO₂: 4.50 SiO₂: 2.25 51 Al₂O₃: 31.20 Al₂O₃:15.60 La₂O₃: 34.00 La₂O₃: 17.00 ZrO₂: 14.80 ZrO₂: 7.40 CaF₂: 20.00 CaF₂:10.00 52 Al₂O₃: 35.73 Al₂O₃: 17.87 La₂O₃: 42.17 La₂O₃: 21.08 ZrO₂: 17.10ZrO₂: 8.55 P₂O₅: 5.00 P₂O₅: 2.50 53 Al₂O₃: 35.73 Al₂O₃: 17.87 La₂O₃:42.17 La₂O₃: 21.08 ZrO₂: 17.10 ZrO₂: 8.55 Nb₂O₅: 5.00 Nb₂O₅: 2.50 54Al₂O₃: 35.73 Al₂O₃: 17.87 La₂O₃: 42.17 La₂O₃: 21.08 ZrO₂: 17.10 ZrO₂:8.55 Ta₂O₅: 5.00 Ta₂O₅: 2.50 55 Al₂O₃: 35.73 Al₂O₃: 17.87 La₂O₃: 42.17La₂O₃: 21.08 ZrO₂: 17.10 ZrO₂: 8.55 SrO: 5.00 SrO: 2.50 56 Al₂O₃: 35.73Al₂O₃: 17.87 La₂O₃: 42.17 La₂O₃: 21.08 ZrO₂: 17.10 ZrO₂: 8.55 Mn₂O₃:5.00 Mn₂O₃: 2.50 57 Al₂O₃: 36.50 Al₂O₃: 18.25 La₂O₃: 43.04 La₂O₃: 21.52ZrO₂: 17.46 ZrO₂: 8.73 Fe₂O₃: 3.00 Fe₂O₃: 1.50 58 Al₂O₃: 36.50 Al₂O₃:18.25 La₂O₃: 43.04 La₂O₃: 21.52 ZrO₂: 17.46 ZrO₂: 8.73 Cr₂O₃: 3.00Cr₂O₃: 1.50 59 CaO: 36.00 CaO: 18.00 Al₂O₃: 44.00 Al₂O₃: 22.00 ZrO₂:20.00 ZrO₂: 10.00 60 La₂O₃: 40.90 La₂O₃: 20.45 Al₂O₃: 40.98 Al₂O₃: 20.49ZrO₂: 18.12 ZrO₂: 9.06 61 SrO: 22.95 SrO: 11.47 Al₂O₃: 62.05 Al₂O₃:31.25 ZrO₂: 15.00 ZrO₂: 7.50 62 La₂O₃: 50.00 La₂O₃: 25.00 Al₂O₃: 22.00Al₂O₃: 11.00 SiO₂: 28.00 SiO₂: 14.00

[0250] Various properties/characteristics of some Example 1-62 materialwere measured as follows. Powder x-ray diffraction (using an x-raydiffractometer (obtained under the trade designation “PHILLIPS XRG 3100”from PHILLIPS, Mahwah, N.J.) with copper K_(α1) radiation of 1.54050Angstrom)) was used to qualitatively measure phases present in examplematerials. The presence of broad diffused intensity peak was taken as anindication of glassy nature of a material. The existence of both broadpeak and well-defined peaks was taken as an indication of existence ofcrystalline matter within an amorphous matrix. Phases detected invarious examples are reported in Table III, below. TABLE III PhysicalCharacteristics of Beads of Examples 1-62 Glass Phases detectedTransition Crystallization Hot-Pressing via x-ray TemperatureTemperature Temperature Example diffraction Color (T_(g), ° C.) (T_(x),° C.) (° C.) 1 Amorphous* Clear 834 932 960 2 Amorphous* Clear 837 936960 3 Amorphous* Clear 831 935 — 4 Amorphous* Clear 843 928 — 5Amorphous* Clear 848 920 960 6 Amorphous* Clear 850 923 — 7 Amorphous*Clear 849 930 — 8 Amorphous* Clear 843 932 — 9 Amorphous* Clear 856 918960 10 Amorphous* Clear/milky 858 914 965 and crystalline 11 Amorphous*Clear/milky 859 914 — and crystalline 12 Amorphous* Clear/milky 862 912— and crystalline 13 Amorphous* Clear/milky 875 908 — and crystalline 14Crystalline and Milky/clear — — — amorphous 15 Crystalline andMilky/clear — — — amorphous 16 Amorphous* Brown 838 908 960 andcrystalline 17 Amorphous* Intense 874 921 975 yellow/ mustard 18Amorphous* Clear 886 933 985 19 Amorphous* Greenish 881 935 985 20Amorphous* Intense pink 885 934 21 Amorphous* Blue/pink 836 930 965fluorescent 22 Amorphous* Yellow 831 934 965 23 Amorphous* Yellow/gold838 929 — 24 Amorphous* Pink 841 932 — 25 Amorphous* Light green 828 937960 26 Amorphous* Clear 795 901 950 27 Amorphous* Clear 780 870 — 28Amorphous* Clear 816 942 950 29 Amorphous* Clear 809 934 950 30Amorphous* Clear/ 840 922 950 greenish 31 Amorphous* Clear 836 934 95032 Amorphous* Clear 832 943 950 33 Amorphous* clear 830 943 950 34Amorphous* Clear/some 818 931 950 green 35 Amorphous* Clear 837 1001 970 36 Amorphous* Clear/milky 874 932 980 and Crystalline 37 Amorphous*Clear/milky 871 934 — and Crystalline 38 Amorphous* Clear/milky 874 937— and Crystalline 39 Amorphous* Clear/milky 870 942 — and Crystalline 40Amorphous* Clear 843 938 970 41 Amorphous* Blue/pink 848 934 970fluorescent 42 Amorphous* Clear/milky 880 943 — and Crystalline 43Amorphous* Pink 876 936 — and Crystalline 44 Amorphous* Clear 821 927970 45 Amorphous* Clear/ 867 948 — and Greenish Crystalline 46Amorphous* Clear/milky 869 934 — and Crystalline 47 Amorphous* Clear 845922 970 48 Amorphous* Clear/milky 870 933 — and Crystalline 49Amorphous* Clear 831 916 970 50 Amorphous* Clear 826 926 970 51Amorphous* Clear — 676 — 52 Amorphous* Clear 857 932 — 53 Amorphous*Clear — — — 54 Amorphous* Clear — — — 55 Amorphous* Clear — — — 56Amorphous* Clear/Brown — — — 57 Amorphous* Clear/grey — — — 58Amorphous* Clear/Green — — — 59 Amorphous* Clear 851 977 975 60Amorphous* Clear 839 932 965 61 Amorphous* Clear 875 934 975 62Amorphous* Clear 842 1085   1050**

[0251] For differential thermal analysis (DTA), a material was screenedto retain amorphous beads (microspheres) in the 90-125 micrometer sizerange. DTA runs were made (using an instrument obtained from NetzschInstruments, Selb, Germany, under the trade designation “NETZSCH STA 409DTA/TGA”). The amount of each screened sample placed in the 100microliter Al₂O₃ sample holder was 400 milligrams. Each sample washeated in static air at a rate of 10° C./minute from room temperature(about 25° C.) to 1200° C.

[0252] Referring to FIG. 3, line 801 is the plotted DTA data for theExample 1 material. Referring to FIG. 3, line 801, the materialexhibited an endothermic event at temperature around 840° C., asevidenced by the downward curve of line 801. It was believed that eventwas due to the glass transition (T_(g)) of the material. At about 934°C., an exothermic event was observed as evidenced by the sharp peak inline 801. It was believed that event was due to the crystallization(T_(x)) of the material. These T_(g) and T_(x) values for other examplesare reported in Table III, above. The hot-pressing temperature at whichappreciable glass flow occurred, as indicated by the displacementcontrol unit of the hot pressing equipment described above, are reportedfor various examples in Table III, above. (In example 63, pressurelesssintering was used.)

Example 63

[0253] About 120 g of the amorphous beads prepared as in Example 1 wereplaced in a graphite die and hot-pressed using uniaxial pressingapparatus (obtained under the trade designation “HP-50”, ThermalTechnology Inc., Brea, Calif.). The hot-pressing was carried out at 960°C. in argon atmosphere and 2 ksi (13.8 MPa) pressure to provide ahot-pressed disk. Holding time at pressure was 30 minutes.

[0254] Two cylinders were core-drilled from the hot-pressed disk andmounted on CEREC-compatible stubs; one was approximately 12 mm indiameter×15 mm in height; the other was approximately 14 mm in diameterand 17 mm in height. The lanthanum oxide/aluminum oxide/zirconium oxidematerial was amorphous (glassy) and dark blue in color.

[0255] A dental coping was milled from the small cylinder on anautomated milling system (available from Sirona Dental Systems,Bensheim, Germany, under the trade designation “CEREC 2”) with LS(LabSide) software; “CEREC 2” employs a 30 mm diametermetal-plated-diamond wheel and a 1.6 mm diameter cylindrical bur. Freshtools and lubricant water were used. The restoration was milled in under20 minutes, and appeared similar in form to the same restoration milledin a commercial block material, PARADIGM MZ100 Block for CEREC(available from 3M Company, St. Paul, Minn.) see FIG. 4.

Example 64

[0256] A billet (approximately 37 mm in diameter and 17 mm in height) ofhot-pressed lanthanum oxide/aluminum oxide/zirconium oxide material wasprepared as in Example 64; a 14 mm diameter×17 mm height cylinder wascore-drilled from the billlet, then prepared for the CEREC by bonding itto a CEREC stub with an epoxy adhesive (available from 3M Company, St.Paul, Minn., under the trade designation “3M DP100”).

[0257] A molar full-occlusion crown was milled from the larger cylinderon the CEREC 3; a new diamond cone and 1.6-mm cylinder tools, and 100 mlof ProCAD DENTATEC Milling Additive (available from Sirona DentalSystems) in the water tank were used. The milled surface appearedidentical to those of a commercial porcelain. The buccal surface waspolished with a finishing brush (available from 3M Company, under thetradename, “SOF-LEX”). The resulting surface was smooth and suitable forocclusal contact.

Example 65

[0258] About 120 g of the amorphous beads prepared as in Example 1 wereplaced in a graphite die and hot-pressed using uniaxial pressingapparatus (obtained under the trade designation “HP-50”, ThermalTechnology Inc., Brea, Calif.). The hot-pressing was carried out at 960°C. in argon atmosphere and 4 ksi (27.6 MPa) pressure. Holding time atpressure was 20 minutes. The resulting disk was core drilled to makefive cylindrical specimens for dental milling evaluations.

Example 66

[0259] About 50 g of the amorphous beads prepared as in Example 1 wereplaced in a graphite die and hot-pressed using uniaxial pressingapparatus (obtained under the trade designation “HP-50”, ThermalTechnology Inc., Brea, Calif.). The hot-pressing was carried out at 925°C. in argon atmosphere and 0.55 ksi (3.8 MPa) pressure. Holding time atpressure was 20 minutes. The resulting disk was core drilled to make onecylindrical specimen (approximately 10 mm in diameter×15 mm in height)for dental milling evaluations. The lanthanum oxide/aluminumoxide/zirconium oxide material was amorphous (glassy) and light yellowexhibiting some opalescence.

[0260] The block was bonded to a CEREC-compatible stub, and thenmachined on a CEREC 3 system (Sirona Dental Systems, Bensheim, Germany)using the set of diamond burs used in Example 65, and 75 ml of SironaProCAD DENTATEC lubricant in a fresh tank of deionized water. 1×4×12 mmbars were machined from the blocks. Visual inspection and the lack oferror messages from the CEREC software indicated that the tools werecapable of further machining. Examples 65 and 66 demonstrate that thematerial can be machined.

[0261] The thermal expansion behavior of Example 67 material wasmeasured on a Seiko Thermomechanical Analyzer at a heating rate of 10°C./min. The coefficient of thermal expansion was 10.3 ppm/° C.; thesoftening point was about 880° C. A 10×10×3 mm disk of Example 66material was heat-treated in a furnace (an electrically heated furnace(obtained under the trade designation “Model KKSK-666-3100” from KeithFurnaces of Pico Rivera, Calif.)) as follows. The disk was first heatedfrom room temperature (about 25° C.) to about 900° C. at a rate of about10° C./min and then held at 900° C. for about 1 hour. Next, the disk washeated from about 900° C. to about 1300° C. at a rate of about 10°C./min and then held at 1300° C. for about 1 hour, before cooling backto room temperature by turning off the furnace. Dimensional shrinkagethat occurred during this heat-treatment was measured to be 4.5%.

Example 67

[0262] About 150 g of the amorphous beads prepared as described inExample 1 were placed in a 5 centimeter (cm)×5 cm×5 cm steel can, whichwas then evacuated and sealed from the atmosphere. The steel can wassubsequently hot-isostatically pressed (HIPed) using a HIP apparatus(obtained under the trade designation “IPS Eagle-6”, American IsostaticPresses Inc., OH). The HIPing was carried out at 207 MPa (30 ksi)pressure in an argon atmosphere. The HIPing furnace was ramped up to970° C. at 25° C./minute and held at that temperature for 30 minutes.After the HIPing, the steel can was cut and the charge material removed.It was observed that amorphous beads had coalesced into a dense body oftransparent, glassy material. The DTA trace, conducted as summarized inExamples 2-62, exhibited a glass transition (T_(g)) of 879° C. and acrystallization temperature (T_(x)) of 931° C.

Example 68

[0263] 35 g of amorphous beads from Example 1, and 15 g of α-Al₂O₃(obtained from Condea Vista, Tucson, Ariz., under the trade designation“APA-0.5”), were placed in a polyethylene bottle. After 80 g ofdistilled water and 300 g of zirconia media (Tosoh Ceramics, BoundBrook, N.J., under the trade designation “YTZ”) was added to the bottle.The mixture was comminuted for 24 hours at 120 rpms. The milled materialwas dried using a heat gun. 20 g of the dried powder was hot-pressed asdescribed in Example 1. The result was an opaque billet.

Example 69

[0264] 20 g of amorphous beads prepared as described in Example 62, and15 g of amorphous beads prepared as described in Example 1, were placedin an alumina crucible and heat-treated in a furnace (an electricallyheated furnace (obtained under the trade designation “ModelKKSK-666-3100”, from Keith Furnaces of Pico Rivera, Calif.)) at 1050° C.for 1 hour. The obtained material was translucent body with beads ofExample 1 evenly distributed through an amorphous matrix of viscouslyflowed amorphous beads of Example 62.

Example 70

[0265] 15 g of amorphous beads prepared as described in Example 1 wereplaced in an alumina crucible and heat-treated in a furnace (anelectrically heated furnace (obtained under the trade designation “ModelKKSK-666-3100” from Keith Furnaces of Pico Rivera, Calif.)) at 1250° C.for 4 hours. The obtained material was easily friable but handleablebody.

[0266] A 1.4 g portion of this porous, bisque-fired body was placed ontoa platinum foil; 0.6 g of a lanthana-alumina-silica glass powder (VITAIN-CERAM Alumina Infiltration Glass, shade All: Vita Zahnfabrik H.Rauter GmbH & Co. KG) was placed on top of the body. The foil, body, andglass powder were then fired in a dental porcelain furnace under vacuumat 1120° C. for 60 minutes. After firing, the body was partiallyinfiltrated with the glass; an additional 0.93 g of glass powder wasplaced on the body, and then fired again per the same condition. Theresulting body was fully infiltrated with the glass.

[0267] A 5×5×5 mm (0.04 g) portion of the porous, bisque-fired body waspartially immersed in a tray of photocurable resin (made by mixing 20.79parts by weight bis-GMA, 29.11 parts UDMA, 29.11 parts Bis-EMA6, 4.16parts TEGDMA, 14.00 parts HEMA, 0.172 parts CPQ, 0.43 parts DPIHFP, 0.86parts EDMAB, 0.086 parts BHT and 1.29 parts NORBLOC 7966). After twohours, the resin was fully infiltrated into the block. The block wasremoved and cured by exposure to light from a 3M Company XL3000 LightCure Unit for 10 seconds, followed by two 90 second cycles in a KulzerDentacolor XS unit (Kulzer, Wehrheim, Germany). The result was a hard,strong, resin-ceramic composite with two interpenetrating phases.

Example 71 Plasma-Spraying

[0268] A 250-ml polyethylene bottle (7.3-cm diameter) was charged withthe following 50-gram mixture: 19.3 g of alumina particles (obtainedfrom Alcoa Industrial Chemicals, Bauxite, Ark., under the tradedesignation “Al6SG”), 9.5 g of zirconium oxide particles (obtained fromZirconia Sales, Inc., of Marietta, Ga. under the trade designation“DK-2”), and 21.2 g of lanthanum oxide particles (obtained from MolycorpInc., Mountain Pass, Calif.), 75 g of isopropyl alcohol, and 200 g ofalumina milling media (cylindrical in shape, both height and diameter of0.635 cm; 99.9% alumina; obtained from Coors, Golden, Colo.). Thecontents of the polyethylene bottle were milled for 16 hours at 60revolutions per minute (rpm). The ratio of alumina to zirconia in thestarting material was 2:1, and the alumina and zirconia collectivelymade up about 58 weight percent (wt-%). After the milling, the millingmedia were removed and the slurry was poured onto a warm (approximately75° C.) glass (“PYREX”) pan and dried. The dried mixture was screenedthrough a 70-mesh screen (212-micrometer opening size) with the aid of apaint brush.

[0269] After grinding and screening, the mixture of milled feedparticles was fed slowly (0.5 gram/minute) into a hydrogen/oxygen torchflame to melt the particles and generate glass beads as described inExample 1. The glass beads were spherical in shape and varied in sizefrom a few micrometers (i.e., microns) up to 250 micrometers.Subsequently, the flame-formed beads having diameters less than 125micrometers were then passed through a plasma gun and deposited onstainless steel substrates as follows.

[0270] Four 304 stainless steel pieces (76.2 millimeter (mm)×25.4mm×3.175 mm dimensions), and two 1080 carbon steel pieces (76.2 mm×25.4mm×1.15 mm) were treated in the following manner. The sides to be coatedwere sandblasted, washed in an ultrasonic bath, and then wiped cleanwith isopropyl alcohol. The four 304 stainless steel and one of the 1080carbon steel substrates were placed approximately 10 centimeters (cm) infront of the nozzle of a plasma gun (obtained under the tradedesignation “Praxair SG-100 Plasma Gun” from Praxair SurfaceTechnologies, Concord, N.H.). The second 1080 carbon steel substrate wasplaced 18 cm in front of the nozzle of the plasma gun. The coatings madeon the second 1080 carbon steel sample at a distance of 18 cm in frontof the nozzle of the plasma gun were not further characterized.

[0271] The plasma unit had a power rating of 40 kW. The plasma gas wasargon (50 pounds per square inch (psi), 0.3 megapascal (MPa)) withhelium as the auxiliary gas (150 psi, 1 MPa). The beads were passedthrough the plasma gun by using argon as the carrier gas (50 psi, 0.3MPa) using a Praxair Model 1270 computerized powder feeder (obtainedfrom Praxair Surface Technologies, Concord, N.H.). During deposition, apotential of about 40 volts and a current of about 900 amperes wasapplied and the plasma gun was panned left to right, up and down, toevenly coat the substrates. When the desired thickness was achieved, theplasma spray was shut off and the samples were recovered. The 1080carbon steel substrate was flexed, thus separating the coating from thesubstrate resulting in a free-standing bulk material. The depositedmaterial had a z dimension (thickness) of about 1350 micrometers, asdetermined using optical microscopy.

[0272] The phase composition (glassy/amorphous/crystalline) wasdetermined through Differential Thermal Analysis (DTA) as describedbelow. The material was classified as amorphous if the corresponding DTAtrace of the material contained an exothermic crystallization event(T_(x)). If the same trace also contained an endothermic event (T_(g))at a temperature lower than T_(x), it was considered to consist of aglass phase. If the DTA trace of the material contained no such events,it was considered to contain crystalline phases.

[0273] Differential thermal analysis (DTA) was conducted using thefollowing method. DTA runs were made (using an instrument obtained fromNetzsch Instruments, Selb, Germany, under the trade designation “NETZSCHSTA 409 DTA/TGA”) using a 140+170 mesh size fraction (i.e., the fractioncollected between 105-micrometer opening size and 90-micrometer openingsize screens). The amount of each screened sample placed in a100-microliter Al₂O₃ sample holder was about 400 milligrams. Each samplewas heated in static air at a rate of 10° C./minute from roomtemperature (about 25° C.) to 1100° C.

[0274] The coated material (on 304 stainless steel substrates) exhibitedan endothermic event at a temperature around 880° C., as evidenced by adownward change in the curve of the trace. It is believed this event wasdue to the glass transition (T_(g)) of the glass material. The samematerial exhibited an exothermic event at a temperature around 931° C.,as evidenced by a sharp peak in the trace. It is believed that thisevent was due to the crystallization (T_(x)) of the material. Thus, thecoated material (on 304 stainless steel substrates) and thefree-standing bulk material were glassy as determined by a DTA trace.

[0275] A portion of the glassy free-standing bulk material was thenheat-treated at 1300° C. for 48 hours. Powder x-ray diffraction, XRD,(using an x-ray diffractometer (obtained under the trade designation“PHILLIPS XRG 3100” from Phillips, Mahwah, N.J.) with copper K_(α1)radiation of 1.54050 Angstrom)) was used to determine the phasespresent. The phases were determined by comparing the peaks present inthe XRD trace of the crystallized material to XRD patterns ofcrystalline phases provided in JCPDS (Joint Committee on PowderDiffraction Standards) databases, published by International Center forDiffraction Data. The resulting crystalline material included LaAlO₃,ZrO₂ (cubic, tetragonal), LaAl₁₁O₁₈, and transitional Al₂O₃ phases.

[0276] Another portion of the glassy free-standing bulk material wascrystallized at 1300° C. for 1 hour in an electrically heated furnace(obtained from CM Furnaces, Bloomfield, N.J., under the tradedesignation “Rapid Temp Furnace”). The crystallized coating was crushedwith a hammer into particles. The fraction that passed through a sievewith a 600-micrometer opening size but did not pass through a screenwith 500-micrometer openings was cleaned of debris by washing in a sonicbath (obtained from Cole-Parmer, Vernon Hills, Ill., under the tradedesignation “8891”) for 15 minutes, dried at 100° C. A portion of theparticles was mounted on a metal cylinder (3 cm in diameter and 2 cmhigh) using carbon tape. The mounted sample was sputter coated with athin layer of gold-palladium and viewed using a JEOL scanning electronmicroscopy (SEM) (Model JSM 840A). The fractured surface was rough andno crystals coarser than 200 nanometers (nm) were observed via SEM.

Example 72

[0277] Feed particles were made as described in Example 71 using thefollowing 50-gram mixture: 21.5 g of alumina particles (obtained fromAlcoa Industrial Chemicals, Bauxite, Ark. under the trade designation“Al6SG”), 9 g of zirconium oxide particles (obtained from ZirconiaSales, Inc. of Marietta, Ga. under the trade designation “DK-2”), and19.5 g of cerium oxide particles (obtained from Rhone-Poulence, France).The ratio of alumina to zirconia in the starting material was 2.4:1 andthe alumina and zirconia collectively made up about 61 weight percent.Feed particles were flame-formed into beads (of a size that varied froma few micrometers up to 250 micrometers) as described in Example 71.Subsequently, the flame-formed beads having diameters between 180micrometers and 250 micrometers were passed through a plasma gun anddeposited on stainless and carbon steel substrates as described inExample 71.

[0278] The coated 1080 carbon steel substrates were flexed, thusseparating the coating from the substrate resulting in a free-standingbulk material. The resulting bulk material had a z dimension (thickness)of about 700 micrometers, as determined using optical microscopy. Themicrostructure was also observed using optical microscopy. The materialconsisted of generally spherical and oblique crystalline particles,which were opaque, within a predominantly amorphous matrix, which wastransparent. Amorphous material is typically transparent due to the lackof light scattering centers such as crystal boundaries, while thecrystalline particles show a crystalline structure and are opaque due tolight scattering effects. The crystalline phases, determined by powderXRD analysis as described in Examples 71, consisted ofZr_(0.4)Ce_(0.6)O₂ (cubic) and transitional Al₂O₃.

[0279] A second deposition experiment was carried out using theflame-formed beads having diameters less than 125 micrometers. Theresulting coating had a z dimension (thickness) of about 1100micrometers, as determined using optical microscopy. The microstructurewas also observed using optical microscopy. This material had similarfeatures (i.e., consisted of generally spherical and oblique crystallineparticles within a predominantly amorphous matrix) to those of thematerial formed from beads having diameters between 180 micrometers and250 micrometers. The crystalline phases, determined by XRD analysis asdescribed in Example 71 consisted of Zr_(0.4)Ce_(0.6)O₂ (cubic) andtransitional Al₂O₃.

Example 73

[0280] Feed particles were made as described in Example 71 using thefollowing 50-gram mixture: 27.9 g of alumina particles (obtained fromAlcoa Industrial Chemicals, Bauxite, Ark. under the trade designation“Al6SG”), 7.8 g of zirconium oxide particles (obtained from ZirconiaSales, Inc., Marietta, Ga. under the trade designation “DK-2”), and 14.3g of yttrium oxide particles (obtained from H. C. Stark Newton, Mass.).The ratio of alumina to zirconia of initial starting materials was 3.5:1and the alumina and zirconia collectively made up about 72 weightpercent. The feed particles were then screened through a 30-mesh screen(600-micrometer opening size) and heat-treated at 1400° C. for 2 hoursin an electrically heated furnace (obtained from CM Furnaces,Bloomfield, N.J., under the trade designation “Rapid Temp Furnace”). Theheat-treated particles were further screened to separate out particleswith diameters between 125 micrometers and 180 micrometers, which werethen passed through a plasma gun and deposited on stainless steelsubstrates as described in Example 71.

[0281] The 1080 carbon steel substrate was flexed, thus separating thecoating from the substrate resulting in a free-standing bulk material.The resulting bulk material had a z dimension (thickness) of about 700micrometers, as determined using optical microscopy. The microstructurewas observed using optical microscopy. This material consisted ofgenerally crystalline opaque particles (which retained their originalshapes) within a predominantly transparent, amorphous matrix. Thecrystalline phases, determined by powder XRD analysis as described inExample 71, consisted of Al₅Y₃O₁₂ and Y_(0.15)Zr_(0.85)O_(1.93).

[0282] Another portion of the free-standing bulk material wascrystallized at 1300° C. for 1 hour and the fractured surface wassputter coated with a thin layer of gold-palladium and viewed using aJEOL SEM (Model JSM 840A), as described above in Example 71. Thefractured surface was rough and no crystals coarser than 200 nm wereobserved.

Example 74

[0283] A thick coating consisting of various layers of the above threeexamples was plasma sprayed using feed particles produced in Examples71-73. The first layer was coated as described in Example 72, the secondas described in Example 71, and the third as described in Example 73.

[0284] The substrate was not sandblasted prior to coating so that it wasremoved easily by plying it apart by hand, resulting in a free-standingbulk material, approximately 75 millimeters (mm)×25 mm×7.5 mm.Cylindrical blocks were prepared by core-drilling through the thickcoating.

[0285] The first layer had a z dimension (thickness) of approximately2.5 mm, as determined using optical microscopy. The microstructure wasobserved using optical microscopy. This material had similar features tothose of the material of Example 72 (i.e., consisted of generallyspherical and opaque crystalline particles within a predominantlytransparent, amorphous matrix). The second layer had a z dimension(thickness) of approximately 2 mm, as determined using opticalmicroscopy. The microstructure was also observed using opticalmicroscopy. This material had similar features to those of the materialof Example 71 (i.e., was transparent suggesting it was amorphous). Thethird layer had a z dimension (thickness) of approximately 3 mm, asdetermined using optical microscopy. The microstructure was alsoobserved using optical microscopy. This material had similar features tothose of the material of Example 73 (i.e., it consisted of generallyopaque crystalline particles (which retained their original shapes)within a predominantly transparent, amorphous matrix).

[0286] The blocks had bands of color ranging from dark umber to lightbeige. Two blocks (approximately 10 mm diameter×15 mm height) werebonded to CEREC-compatible stubs, then machined on a CEREC 3 system(Sirona Dental Systems, Bensheim Germany) using a new set of diamondburs and 75 ml of Sirona ProCAD Dentatec lubricant in a fresh tank ofdeionized water. A molar crown was machined from one block; a coping fora maxillary lateral was machined from the other. No problems wereencountered in machining. The resulting units were well machined. Thisexample demonstrates that a plasma-sprayed embodiment of the inventioncan be made and machined, and also a multicolored block can be made.

Example 75

[0287] Nanoparticulates of La₂O₃—Al₂O₃—ZrO₂ (LAZ) and CeO₂—Al₂O₃—ZrO₂(CAZ) materials the compositions shown in Table IV were preparedaccording to the method disclosed in U.S. Pat. No. 5,958,361 (Laine etal). TABLE IV Material CeO₂ La₂O₃ Al₂O₃ ZrO₂ LAZ NA 42.50 38.75 18.75CAZ 39.00 NA 43.00 18.00

[0288] Other processes such as those described in U.S. Pat. Nos.5,075,090, (Lewis et al) and 5,358,695 (Helble et al) can also be usedto produce particulates useful in this example.

[0289] Powder x-ray diffraction, XRD, (using an x-ray diffractometer(obtained under the trade designation “PHILLIPS XRG 3100” from Phillips,Mahwah, N.J.) with copper K_(α1) radiation of 1.54050 Angstrom) was usedto determine the phases present. The phases were determined by comparingthe peaks present in the XRD trace of the crystallized material to XRDpatterns of crystalline phases provided in JCPDS (Joint Committee onPowder Diffraction Standards) databases, published by InternationalCenter for Diffraction Data. The resulting phases are reported in TableV. TABLE V XRD Analysis of Crystalline Phases Identified Phases/RelativeIntensities La₂O₃—Al₂O₃—ZrO₂ Amorphous + LaAlO₃ (D_(app) = 580 Å)/100 +(LAZ) “La_(0.25)Zr_(0.75)O_(1.875)”/37 + transitional Al₂O₃/18CeO₂—Al₂O₃—ZrO₂ “Zr_(0.4)Ce_(0.6)O₂” (cubic, a₀ ≈ 5.30 Å) (D_(app) = 240Å)/100 + transitional Al₂O₃/6 + (possible CeAlO₃)/5

[0290] 5.570 g of LAZ powder was treated with 5.570 g of a silane agent(3M Company RELY X Ceramic Primer), allowed to dry; 3.618 g of theresulting powder was then blended with 2.59 g of the photocurable resinmade by blending 24.18 parts by weight of bis-GMA, 33.85 parts UDMA,33.85 parts bis-EMA6, 4.84 parts TEGDMA, 0.2 parts CPQ, 0.5 parts DPHFP,1.0 parts EDMAB, 0.1 parts BHT, and 1.5 parts of NORBLOCK 7966. Theresulting composite was white in color and had viscosity and handlingsuitable for a flowable style dental composite. The composite was filledinto a mold 2 mm deep by 5 mm diameter, in two increments of 1 mm, eachcured for 60 seconds with a 3M Company XL3000 Dental Curing Light. Thehardness of the cured composite was measured with a Barcol Hardnessmeter, models GYZJ-934-1 (Barber Coleman, Inc., Loves Park, Ill.). Anaverage Barcol Hardness of 91±0.6 was measured on the top surface of thecured composite.

[0291] An intracoronal inlay on a molar tooth was prepared in a gypsumdental model. The composite was loaded into the preparation in several1-mm increments, each cured for 60 seconds with a 3M Company XL3000Dental Curing Light; in the final increment, occlusal anatomy wassculpted into the composite before curing. The resulting inlay wasesthetic.

Example 76

[0292] 84.9 g of aluminum formoacetate were charged to a Pyrex beaker,which was then placed on a hotplate/stirred with a Teflon-coated stirbar; 16.5 g of zirconyl acetate (Magnesium Elektron Inc.) were addedunder vigorous stirring to form a clear, slightly turbid sol, followedby 22.5 g of lanthanum nitrate (Johnson Matthey #12915, 99.9%). Theingredients blended readily to form a clear, slightly turbid, opalescentsol with no precipitates, gelation, or thickening, suitable for furtherprocesses such as flame-spraying, spray-drying, coating, spraypyrolysis, gelation/drying/calcinations, gelation/autoclaving, orcontrolled precipitation of particles. The sol was calculated to have anominal yield of 20 g of oxide of composition La₂O₃ 42.3 wt-%, Al₂O₃39.2 wt-%, ZrO₂ 18.5 wt-%. 9.1 g of polyethylene glycol MW=400 (PEG₄₀₀:Union Carbide Carbowax, Sentry Grade) was added to the sol; a small vialof this PEG-doped sol was saved to observe stability. This sol wasstable for 8 hours, but developed white gel precipitates after 24 hours.To the remaining sol was added 10.8 g of the liquid component ofVITREMER CORE Restorative liquid (available from 3M Company, St. Paul,Minn.), which formed a soft solid mass in 3 hours. This soft solid masswas dried at 100° C./5 hrs. TG/DTA analysis of the dried material showedweight loss below about 500° C. due to water evaporation and pyrolysisof the organics and nitrates/acetates. Exotherm peaks at 208° C. and372° C. are due to the pyrolysis. Surprisingly, there were no endothermsfrom crystallization up to as high as 1300° C.; the resulting powder waswhite. Samples of the dried sol were calcined at 550° C./4 hr and 850°C./4 hr; the results (Table VI) show a large amorphous portion, and somecrystalline phases. TABLE VI XRD Results Description IdentifiedPhases/Relative Intensities LAZ sol-gel, calcined at 550° C.;La₂O₂CO₃/100 + Grey, granular powder La₂CO₅/65 + amorphous LAZ sol-gel,calcined at 850° C.; La₂O₃/100 + La(OH)₃/52 + Off-white, granular powderLaAlO₃/48 + amorphous

[0293] 2.90 g of the powder was treated with 2.9 g of a silane agent (3MCompany RELYX Ceramic Primer), allowed to dry, and then blended with 2.9g of photocurable resin (made by blending 24.18 parts by weight bis-GMA,33.85 parts UDMA, 33.85 parts Bis-EMA6, 4.84 parts TEGDMA, 0.2 partsCPQ, 0.5 parts DPHFP, 1.0 parts EDMAB, 0.1 parts BHT and 1.5 partsNORBLOC 7966)). The resulting composite was ivory in color and hadviscosity and handling suitable for a flowable style dental composite.The composite was filled into a mold 2 mm deep by 5 mm diameter, in twoincrements of 1 mm, each cured for 60 seconds with a 3M Company XL3000Dental Curing Light. The hardness of the cured composite was measuredwith a Barcol Hardness meter, models GYZJ-934-1 (Barber Coleman, Inc.,Loves Park, Ill.). An average Barcol Hardness of 91+1 was measured onthe top surface of the cured composite.

Example 77

[0294] 42.6 parts by weight (pbs) of aluminum formoacetate were chargedto a Pyrex beaker, which was then placed on a hotplate/stirred with aTeflon-coated stir bar; 8.3 pbw of zirconyl acetate (Magnesium ElektronInc.) were added under vigorous stirring, followed by 11.3 pbw oflanthanum nitrate (Johnson Matthey #12915, 99.9%), then 0.6 pbw ofpolyethylene glycol MW=400 (PEG₄₀₀: Union Carbide Carbowax, SentryGrade), and sufficient nitric acid to reduce the pH from ˜4.4 to ˜3-3.3.The ingredients blended readily to form a clear, slightly turbid,opalescent sol with no precipitates, gelation, or thickening, suitablefor further processes such as flame-spraying, spray-drying, coating,spray pyrolysis, gelation/drying/calcinations, gelation/autoclaving, orcontrolled precipitation of particles. The sol was calculated to have acomposition La₂O₃ 42.3 wt-%, Al₂O₃ 39.2 wt-%, ZrO₂ 18.5 wt-%. The solwas spray-dried immediately after mixing to a fine, free-flowing powderin a Buchi spray dryer. TG/DTA analysis of the dried material showsweight loss below circa 500° C. due to water evaporation and pyrolysisof the organics and nitrates/acetates. An exotherm peaks at 100.7° C.can be attributed to water evaporation, and 348.7° C. to the pyrolysisof the organics. Surprisingly, there are no endotherms fromcrystallization up to as high as 1300° C.; the resulting powder waswhite.

[0295] A small sample of an identically blended sol was retained toobserve stability; another small sample was diluted with water by mixing2.3 g of sol and 1.7 g deionized water. Both sols were stable at 15 hr;the undiluted sol developed a fine layer of white precipitate by circa40 hours, while the diluted sol was free of precipitates, gelation, orthickening after 5 days.

[0296] A sample of this powder was calcined at 550° C. for 1 hour in air(resultant powder was white) and hot-pressed at 970° C. as described inExample 1; XRD on resulting semi-solid disk showed that the majorcrystalline phase present was a face-centered cubic (FCC) crystalstructure with a lattice parameter of ˜5.28 Å, most likely due to astabilized form of zirconia. A possible transitional alumina phase wasalso observed, as well as an unidentified phase(s) with diffractionpeaks at d-spacings of ˜4.1 Å and ˜3.7 Å. The powder was then fired at700° C./4 hr; the resulting white powder was crushed in a mortar andpestle.

Example 78

[0297] 84.9 g of aluminum formoacetate were charged to a PYREX beaker,which was then placed on a hotplate/stirrer with a Teflon-coated stirbar; 16.6 g of zirconyl acetate were added under vigorous, followed by87.3 g deionized water, 22.5 g of lanthanum nitrate hexahydrate, 1.8 gpolyethylene glycol (MW=400), and 3.6 g nitric acid. The ingredientsblended readily to form a clear, slightly turbid, opalescent sol with noprecipitates, gelation, or thickening, suitable for further processessuch as flame-spraying, spray-drying, coating, spray pyrolysis, orcontrolled precipitation. The sol was calculated to have a nominal yieldof 42.3 wt-% La₂O₃, 39.2% Al₂O₃, and 18.5% ZrO₂.

[0298] The sol was applied to the following substrates with a cottonswab:

[0299] A. glass slide: 1 coat, dry in air

[0300] B. glass slide: 1 coat, dry with compressed air

[0301] C. glass slide: 4 coats, dried in air between coats

[0302] D. opaque aluminum oxide wafer: 1 coat, dry in air

[0303] E. translucent alumina wafer: 1 coat, dry in air

[0304] F. translucent alumina wafer: 1 coat, dry in air (thicker layer)

[0305] G. glass slide: swipe several lines, dry in air

[0306] The coated substrates were fired at 550° C./2 hr. Samples (B),(E), (G) were clear and well-bonded; the others were black and flaky.The remaining sol was stored under ambient storage conditions in asealed vial; after 13 days the sol remained free of precipitates,gelation, separation, or thickening.

Example 79

[0307] The samples of Example 78 were additionally fired at 560° C. for8 hours. On samples where the brushed sol coating was thick, the firedcoating was dark brown and could be rubbed off; on samples where thebrushed sol coating was thin (because of compressed air drying, orbarely-wet brush), the coating was clear and well-bonded. The sol hasbeen stable for 13 days to date, with no precipitates, gelation, orthickening.

[0308] The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art and are foreseeable without departing from thescope and spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of theinvention intended to be limited only by the claims set forth herein asfollows.

What is claimed is:
 1. An article comprising at least one of a glass orglass-ceramic comprising: a) at least 35 percent by weight Al₂O₃, basedon the total weight of the glass or glass-ceramic, and a first metaloxide other than Al₂O₃, wherein the glass or glass-ceramic contains notmore than 10 percent by weight collectively B₂O₃, GeO₂, P₂O₅, SiO₂,TeO₂, and V₂O₅, based on the total weight of the glass or glass-ceramic;b) at least 35 percent by weight Al₂O₃, based on the total weight of theglass or glass-ceramic, and a first metal oxide other than Al₂O₃,wherein the Al₂O₃ and the first metal oxide, and second metal oxidecollectively comprise at least 70 percent by weight of the glass orglass-ceramic; c) Al₂O₃ and at least one of REO or Y₂O₃, wherein atleast 80 percent by weight of the glass or glass-ceramic collectivelycomprises the Al₂O₃ and the at least one of REO or Y₂O₃, based on thetotal weight of the glass or glass-ceramic; d) Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ orHfO₂, based on the total weight of the glass or glass-ceramic; e) Al₂O₃and at least one of REO or Y₂O₃, wherein at least 60 percent by weightof the glass or glass-ceramic collectively comprises the Al₂O₃ and theat least one of REO or Y₂O₃, and wherein the glass or glass-ceramiccontains not more than 20 percent by weight SiO₂ and not more than 20percent by weight B₂O₃, based on the total weight of the glass orglass-ceramic; f) Al₂O₃, at least one of REO or Y₂O₃, and at least oneof ZrO₂ or HfO₂, wherein at least 60 percent by weight of the glass orglass-ceramic collectively comprises the Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; g) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass or glass-ceramiccomprise the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass or glass-ceramic contains not more than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass or glass-ceramic; h) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or i) a glass-ceramic having an average hardness of atleast 13 GPa, wherein the glass-ceramic has x, y, and z dimensions eachperpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm, and wherein said article is in the form ofa dental article or orthodontic appliance.
 2. The article of claim 1wherein the dental article is selected from the group consisting ofrestoratives, replacements, inlays, onlays, veneers, full and partialcrowns, bridges, implants, implant abutments, copings, anteriorfillings, posterior fillings, and cavity liner, and bridge frameworks.3. The article of claim 1 wherein the orthodontic appliance is selectedfrom the group consisting of brackets, buccal tubes, cleats, andbuttons.
 4. A dental material comprising a mixture of a hardenable resinand a glass or glass-ceramic comprising at least one of: a) at least 35percent by weight Al₂O₃, based on the total weight of the glass orglass-ceramic, and a first metal oxide other than Al₂O₃, wherein theglass or glass-ceramic contains not more than 10 percent by weightcollectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the totalweight of the glass or glass-ceramic; b) at least 35 percent by weightAl₂O₃, based on the total weight of the glass or glass-ceramic, and afirst metal oxide other than Al₂O₃, wherein the Al₂O₃ and the firstmetal oxide, and second metal oxide collectively comprise at least 70percent by weight of the glass or glass-ceramic; c) Al₂O₃ and at leastone of REO or Y₂O₃, wherein at least 80 percent by weight of the glassor glass-ceramic collectively comprises the Al₂O₃ and the at least oneof REO or Y₂O₃, based on the total weight of the glass or glass-ceramic;d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 80 percent by weight of the glass or glass-ceramiccollectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, based on the total weight of the glass orglass-ceramic; e) Al₂O₃ and at least one of REO or Y₂O₃, wherein atleast 60 percent by weight of the glass or glass-ceramic collectivelycomprises the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass or glass-ceramic contains not more than 20 percent by weight SiO₂and not more than 20 percent by weight B₂O₃, based on the total weightof the glass or glass-ceramic; f) Al₂O₃, at least one of REO or Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 60 percent by weightof the glass or glass-ceramic collectively comprises the Al₂O₃, at leastone of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein theglass or glass-ceramic contains not more than 20 percent by weight SiO₂and not more than 20 percent by weight B₂O₃, based on the total weightof the glass or glass-ceramic; g) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass or glass-ceramiccomprise the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass or glass-ceramic contains not more than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass or glass-ceramic; h) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or i) a glass-ceramic having an average hardness of atleast 13 GPa.
 5. The dental material of claim 4 wherein the dentalmaterial is selected from the group consisting of dental restoratives,dental adhesives, dental filler, dental mill blanks, dental prosthesis,dental casing materials, and dental coatings.
 6. The dental material ofclaim 4 wherein the hardenable resin is selected from the groupconsisting of a curable monomer, oligomer, or polymer, and combinationsthereof.
 7. The dental material of claim 4 wherein the glass orglass-ceramic is in the form of particles, nanoclusters, fibers, flakes,whiskers, block, beads, or combinations thereof.
 8. A method of making adental article or an orthodontic appliance comprising the steps of:providing a dental or orthodontic mill blank; carving a dental ororthodontic mill blank, wherein the dental mill blank comprises a glassor glass-ceramic comprising at least one of: a) at least 35 percent byweight Al₂O₃, based on the total weight of the glass or glass-ceramic,and a first metal oxide other than Al₂O₃, wherein the glass orglass-ceramic contains not more than 10 percent by weight collectivelyB₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass or glass-ceramic; b) at least 35 percent by weight Al₂O₃, based onthe total weight of the glass or glass-ceramic, and a first metal oxideother than Al₂O₃, wherein the Al₂O₃ and the first metal oxide, andsecond metal oxide collectively comprise at least 70 percent by weightof the glass or glass-ceramic; c) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 80 percent by weight of the glass or glass-ceramiccollectively comprises the Al₂O₃ and the at least one of REO or Y₂O₃,based on the total weight of the glass or glass-ceramic; d) Al₂O₃, atleast one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 percent by weight of the glass or glass-ceramic collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass or glass-ceramic;e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60 percent byweight of the glass or glass-ceramic collectively comprises the Al₂O₃and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; f) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; g) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass or glass-ceramiccomprise the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass or glass-ceramic contains not more than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass or glass-ceramic; h) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or i) a glass-ceramic having an average hardness of atleast 13 GPa.
 9. The method of claim 8 further comprising the step ofheat treating.
 10. Method of making a dental article or an orthodonticappliance comprising the steps of: heating glass or a glass performabove the T_(g) of the glass such that the glass coalesces or the glassperform flows to form a dental article or an orthodontic appliancehaving a shape; and cooling the coalesced article, wherein the glasscomprises at least one of: a) at least 35 percent by weight Al₂O₃, basedon the total weight of the glass, and a first metal oxide other thanAl₂O₃, wherein the glass or glass-ceramic contains not more than 10percent by weight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅,based on the total weight of the glass; b) at least 35 percent by weightAl₂O₃, based on the total weight of the glass, and a first metal oxideother than Al₂O₃, wherein the Al₂O₃ and the first metal oxide, andsecond metal oxide collectively comprise at least 70 percent by weightof the glass; c) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least80 percent by weight of the glass collectively comprises the Al₂O₃ andthe at least one of REO or Y₂O₃, based on the total weight of the glass;d) Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass; e) Al₂O₃ and atleast one of REO or Y₂O₃, wherein at least 60 percent by weight of theglass collectively comprises the Al₂O₃ and the at least one of REO orY₂O₃, and wherein the glass contains not more than 20 percent by weightSiO₂ and not more than 20 percent by weight B₂O₃, based on the totalweight of the glass; f) Al₂O₃, at least one of REO or Y₂O₃, and at leastone of ZrO₂ or HfO₂, wherein at least 60 percent by weight of the glasscollectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, and wherein the glass contains not more than20 percent by weight SiO₂ and not more than 20 percent by weight B₂O₃,based on the total weight of the glass; g) Al₂O₃ and at least one of REOor Y₂O₃, wherein at least 60 percent by weight of the glass comprise theAl₂O₃ and the at least one of REO or Y₂O₃, and wherein the glasscontains not more than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass; or h) Al₂O₃, at least oneof REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60percent by weight of the glass collectively comprises the Al₂O₃, atleast one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and whereinthe glass contains not more than 40 percent by weight collectively SiO₂,B₂O₃, and P₂O₅, based on the total weight of the glass.
 11. The methodof claim 10 wherein the glass is in the form of nanoclusters, fibers,flakes, whiskers, beads, block, or combinations thereof.
 12. The methodof claim 10 further comprising the step of heat treating the shapedarticle.
 13. A method of making a dental article or an orthodonticappliance comprising the steps of: combining a glass or glass-ceramicwith a hardenable resin to form a mixture; forming the dental article orthe orthodontic appliance into a shape; hardening said mixture to formthe dental article or orthodontic appliance, wherein said glass orglass-ceramic comprises at least one of: a) at least 35 percent byweight Al₂O₃, based on the total weight of the glass or glass-ceramic,and a first metal oxide other than Al₂O₃, wherein the glass orglass-ceramic contains not more than 10 percent by weight collectivelyB₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass or glass-ceramic; b) at least 35 percent by weight Al₂O₃, based onthe total weight of the glass or glass-ceramic, and a first metal oxideother than Al₂O₃, wherein the Al₂O₃ and the first metal oxide, andsecond metal oxide collectively comprise at least 70 percent by weightof the glass or glass-ceramic; c) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 80 percent by weight of the glass or glass-ceramiccollectively comprises the Al₂O₃ and the at least one of REO or Y₂O₃,based on the total weight of the glass or glass-ceramic; d) Al₂O₃, atleast one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 percent by weight of the glass or glass-ceramic collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass or glass-ceramic;e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60 percent byweight of the glass or glass-ceramic collectively comprises the Al₂O₃and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; f) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; g) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass or glass-ceramiccomprise the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass or glass-ceramic contains not more than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass or glass-ceramic; h) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or i) a glass-ceramic having an average hardness of atleast 13 GPa.
 14. A method of making a dental article or orthodonticappliance comprising the steps of: plasma or thermally sprayingparticles comprising metal oxide sources onto a suitable substrate suchthat the particles coalesce to form a shaped article; and optionallyseparating the shaped article or appliance from the substrate, whereinthe shaped article comprises at least one glass of: a) at least 35percent by weight Al₂O₃, based on the total weight of the glass, and afirst metal oxide other than Al₂O₃, wherein the glass contains not morethan 10 percent by weight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, andV₂O₅, based on the total weight of the glass; b) at least 35 percent byweight Al₂O₃, based on the total weight of the glass, and a first metaloxide other than Al₂O₃, wherein the Al₂O₃ and the first metal oxidecollectively comprise at least 70 percent by weight of the glass; c)Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80 percent byweight of the glass collectively comprises the Al₂O₃ and the at leastone of REO or Y₂O₃, based on the total weight of the glass; d) Al₂O₃, atleast one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 percent by weight of the glass collectively comprises theAl₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,based on the total weight of the glass; e) Al₂O₃ and at least one of REOor Y₂O₃, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass contains not more than 20 percent by weight SiO₂ and not more than20 percent by weight B₂O₃, based on the total weight of the glass; f)Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, and wherein the glass contains not more than 20 percent byweight SiO₂ and not more than 20 percent by weight B₂O₃, based on thetotal weight of the glass; g) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass comprise the Al₂O₃and the at least one of REO or Y₂O₃, and wherein the glass contains notmore than 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, basedon the total weight of the glass; or h) Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 percent byweight of the glass collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glasscontains not more than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass.
 15. A kit comprising aplurality of orthodontic or dental components, wherein at least one ofthe components includes a dental material, dental article, or anorthodontic appliance which comprises a glass or glass-ceramiccomprising: a) at least 35 percent by weight Al₂O₃, based on the totalweight of the glass or glass-ceramic, and a first metal oxide other thanAl₂O₃, wherein the glass or glass-ceramic contains not more than 10percent by weight collectively B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅,based on the total weight of the glass or glass-ceramic; b) at least 35percent by weight Al₂O₃, based on the total weight of the glass orglass-ceramic, and a first metal oxide other than Al₂O₃, wherein theAl₂O₃ and the first metal oxide, and second metal oxide collectivelycomprise at least 70 percent by weight of the glass or glass-ceramic; c)Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 80 percent byweight of the glass or glass-ceramic collectively comprises the Al₂O₃and the at least one of REO or Y₂O₃, based on the total weight of theglass or glass-ceramic; d) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 80 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weightof the glass or glass-ceramic; e) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass or glass-ceramiccollectively comprises the Al₂O₃ and the at least one of REO or Y₂O₃,and wherein the glass or glass-ceramic contains not more than 20 percentby weight SiO₂ and not more than 20 percent by weight B₂O₃, based on thetotal weight of the glass or glass-ceramic; f) Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60percent by weight of the glass or glass-ceramic collectively comprisesthe Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ orHfO₂, and wherein the glass or glass-ceramic contains not more than 20percent by weight SiO₂ and not more than 20 percent by weight B₂O₃,based on the total weight of the glass or glass-ceramic; g) Al₂O₃ and atleast one of REO or Y₂O₃, wherein at least 60 percent by weight of theglass or glass-ceramic comprise the Al₂O₃ and the at least one of REO orY₂O₃, and wherein the glass or glass-ceramic contains not more than 40percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the totalweight of the glass or glass-ceramic; h) Al₂O₃, at least one of REO orY₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 percent byweight of the glass or glass-ceramic collectively comprises the Al₂O₃,at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, andwherein the glass or glass-ceramic contains not more than 40 percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe glass or glass-ceramic; or i) a glass-ceramic having an averagehardness of at least 13 GPa.
 16. The kit of claim 15 further comprisinga component selected from the group consisting of an orthodonticadhesive, an adhesive primer, an appliance-positioning tool, andcombinations thereof.
 17. The kit of claim 15 further comprising acomponent selected from the group consisting of a dental mill blank, abonding agent, a milling lubricant, a color-matching compositionsuitable for using in an oral environment, an impression material, aninstrument, a dental composite, a dental porcelain, an abrasive, andcombinations thereof.
 18. A method of performing a dental restorationcomprising the steps of: preparing a dental site to be restored; andapplying a restorative material comprising a glass or glass-ceramiccomprising at least one of: a) at least 35 percent by weight Al₂O₃,based on the total weight of the glass or glass-ceramic, and a firstmetal oxide other than Al₂O₃, wherein the glass or glass-ceramiccontains not more than 10 percent by weight collectively B₂O₃, GeO₂,P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass orglass-ceramic; b) at least 35 percent by weight Al₂O₃, based on thetotal weight of the glass or glass-ceramic, and a first metal oxideother than Al₂O₃, wherein the Al₂O₃ and the first metal oxide, andsecond metal oxide collectively comprise at least 70 percent by weightof the glass or glass-ceramic; c) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 80 percent by weight of the glass or glass-ceramiccollectively comprises the Al₂O₃ and the at least one of REO or Y₂O₃,based on the total weight of the glass or glass-ceramic; d) Al₂O₃, atleast one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 percent by weight of the glass or glass-ceramic collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass or glass-ceramic;e) Al₂O₃ and at least one of REO or Y₂O₃, wherein at least 60 percent byweight of the glass or glass-ceramic collectively comprises the Al₂O₃and the at least one of REO or Y₂O₃, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; f) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 20 percent by weight SiO₂ and notmore than 20 percent by weight B₂O₃, based on the total weight of theglass or glass-ceramic; g) Al₂O₃ and at least one of REO or Y₂O₃,wherein at least 60 percent by weight of the glass or glass-ceramiccomprise the Al₂O₃ and the at least one of REO or Y₂O₃, and wherein theglass or glass-ceramic contains not more than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass or glass-ceramic; h) Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass or glass-ceramic collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and wherein the glass orglass-ceramic contains not more than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass orglass-ceramic; or i) a glass-ceramic having an average hardness of atleast 13 GPa.
 19. The method of claim 18 wherein the restorativematerial is selected from the group consisting of veneers, crowns,inlays, onlays, bridge structures, and combinations thereof.